As mentioned in another post, the prophecy that Davros talks about is only about a hybrid warrior. He interprets it as a Dalek/Time Lord hybrid but based on what we have seen and what he said of the prophecy we don't know if that is correct. Frankly, it would seem a bit pedestrian and unlike Moffat to set up a mystery (which is certainly how it sounded) only to explain it almost immediately. It might be that, but it is far from clear cut.

As for Ashildr, we were primed to notice any more mentions of a hybrid, and when it was mentioned the Doctor said the word in a rather pronounced manner while looking ominous and serious. Also that episode happened to be co-written by Moffat making the chances of any series arc elements that much more likely.

So the way it was initially explained (a rather vague description of a prophecy with nothing definitive other than "hybrid warrior") suggests we are meant to speculate. Classic Moffat tactic. It could still be that it is the Dalek/Time Lord explanation although for me that seems a bit lame. It could be that it is Ashildr. Or, perhaps even more likely, both of those are red herrings and the hybrid has not even appeared yet. That would be quite similar to some things that Moffat has done before. Whatever the solution I don't agree that anything is obvious at this point and the speculation seems entirely reasonable.

Ooh in that case could the hybrid warrior be Orson Pink?! Seems there is still a story there with Orson Pink.. He seemed warrior like roaring in to save the day. Time traveller as he mentioned relatives.. If so we should see an ending for Clara that allows for babies to be made somehow

Nope. Going off on a tangent. I certainly think that Ashildr will hold a lot of cards in future episodes.

Interesting topic. To me the vague hints of a general arc seem to be:

What does the doctor do when thinking he is dying soon? Make a confession?

How does the doctor deal with a grieving companion who has become an adrenaline junkie to cope?

How do those the doctor has "gifted" live their lives?

What is the fallout of hybridization of species the doctor has interacted with?

I see it completely the other way around. I perceived that Moffat dropped a bombshell of sorts by stating the possibility of a dalek/time lord hybrid out there, and I would think/hope that he wouldn't have added such a thing to have it just lead to nothing.

The ashildr mention of the word however, I feel was a red herring to trick people into think of ashildr as possibly being the hybrid in question, just purely because they had heard the word 'hybrid' for the second time. Think about it, the mention of the hybrid project in the opening story is the only reason we think of the word hybrid as being significant at all. Had the doctor described ashildr as a hybrid in the viking story as he did, without it being mentioned in the opening story, no-one would have batted an eyelid or thought anything of it.

We can't know anything for sure, but for me, if the hybrid turns out to be ashildr, that would be pretty boring. For one thing, since she's already been described as such, it wouldn't exactly be 'oh wow, she is the hybrid in question', but to me it would feel like 'oh, is that it?. Secondly, we've already had a part human, part timelord with River, Donna, doctor 10.5, so it wouldn't exactly be breaking new ground, and I would wonder why they had described something so interesting and unique as a half dalek, half time lord, just to then do nothing with it.

Reviving this thread rather than starting a new one on the same subject.

Surprised to see that no-one has really been talking about 'the catastrophe' that was foreshadowed last night. Sounds very much like another piece of the arc puzzle.

So now we have:

The hybrid
the minister of war
Ashildr
The catastrophe

and also

does anyone think they are closer to some sort of theory on what the arc and subsequent finale might look like or contain within?

The 'minister of war', 'the catastrophe' and the presence of ashildr all seem to suggest it will be modern day earth, but what I mentioned in the spoiler tags obviously suggests otherwise. I suspect it will be split between the two personally, but other than that, I'm baffled as to how it might all fit together.

OK, this is my theory. The references that have been repeatedly made are

1. The hybrid Dalek and time Lord
2. Friend or foe
3. Dreaming
4. Bootstrap paradox
5. Clara becoming the doctor

Clara is the hybrid - she was inside the Dalek in episode 2 when the doctor allowed some of his regeneration powers to be used to 'feed' the daleks. Clara was wired up to the Dalek so at that moment she became the hybrid as she received both timelord and Dalek life-force (for want of a better word). The doctor realised this which is why he said he was so sorry when he opened up the casing to release clara. so this raises the question of whether clara is now friend or foe - if the Dalek side of her appears, she would be classed as an enemy? The Bootstrap paradox fits in as the doctor realises that oswin oswald is in fact clara herself and not a splinter. As she is a hybrid, it's the reason that they Convert her fully into a Dalek as they recognise she already has part of their technology. Maybe this means that the doctor wipes her memory and places her in the future as oswin the waitress and encourages her to leave her job to go and see space? He will feel torn because he knows what he is doing to clara but in a sense it has already happened and so he has no choice? The confessional opens when a timelord is about to die - what if it's not the doctor that is going to die but clara (hybrid timelord). He spoke in sleep no more about the need to dream to escape the monsters and stay safe - this is what oswin did in asylum of the daleks. I think he is forewarning her of what is to come. Added to this is the fact that the morpheus pod pulled clara in and the doctor said it sensed she needed to sleep - again, a forewarning perhaps.

Sorry if the above seems a bit disjointed - it makes sense in my head but I'm not sure I've explained it properly!

Is it safe to say this is the most mysterious New Who finale yet as far as knowing what to expect prior to broadcast? Certainly feels that way.

I'd say so. Only the series 4 arc felt anything like this. Just hope the payoff is as good as it was then.

1 - No - that version of a hybrid was mentioned once. The term 'hybrid' has been mentioned more than once, but in relation to actual and perceived hybrids that are not Dalek/Time Lord. It could well be the Clara/Dalek hybrid to which they refer (although I personally doubt it, but if your evidence is the repeated use of the reference, it's simply not there!

4 - Again, not a repeated reference. Really only used so far in the episode that was a Bootstrap Paradox. So entirely in cobtext.

The other three are rather interesting in themselves anyway...

Other things that are unique to this series and have recurred in several episodes are the sonic sunglasses and the guitar. Have we perhaps spent too much time wincing/rejoicing at their existence as an apparent attempt to give Capaldi's Doctor more colour, and too little considering how they might fit into the larger scheme of things?

Good point, I think you are right and they must have some greater significance