Decided that I couldn't stay away!
Been doing some thinking. Caution with MAJOR Spoilers from the OP plus my own theory coming up.
Weeks 3-7
The teams next week are:
Tenacity
Katie (PM)
Jemma
Ella Jade
Pamela
Sarah
Lauren
Steven
Felipe
Daniel
Summit
Roisin (PM)
Nurun
Lindsay
Bianca
James
Mark
Solomon
Sanjay
The teams, by Week 8 are apparently:
Team 1
Katie
Daniel
Mark
Felipe
Team 2
Solomon
James
Sanjay
Bianca
Roisin
Considering ALL of Team 2 are on Summit in Week 3 and 3 out of 4 of Team 1 are on Tenacity in Week 3, I think its a fair bet that Team 1 are Tenacity and Team 2 are Summit.
Interestingly, though Summit lose next week, 6 out of 8 of them are still on board by Week 8, meaning, assuming there are no major reshuffles, only Lindsay and Nurun can get fired from that team in this time.
By contrast, on Tenacity, only 3 of their 9 are still around by Week 8, meaning that they must surely lose the bulk of the upcoming tasks, especially if Week 3 is a double firing of Lindsay and Nurun as some have speculated. In fact, if the above two are fired in Week 3, then then only one who can get fired from Summit until Week 8 is the person who goes over to level the teams in Week 4 (Considering Summit will be at least 2 candidates, maybe 3 candidates down by this point)
The main spanner in the works is that apparently, Sanjay is on a sub-team with Pamela and Katie in Week 6, which makes little sense unless Tenacity lose both Week 4 and 5 and Sanjay is ported over. Not sure how he returns to Summit or how Mark ends up on Tenacity though (Unless its like a Myles-style deal where Lord Sugar just moves him over for the fun of it)
However, most of the evidence points to Summit winning the bulk of the upcoming tasks. This is supported by the fact that they have the extra member in Week 8.
It is virtually certain though, that we can expect a lot of multiple firings in this period - 9 candidates by Week 8 is almost back on track (In Series 8, there were 9 candidates left in Week 8) and this could well account for the seemingly-bizarre team switches.
Week 8 and Beyond
After Week 8, there can be no sub-teams of 3 (As the sub-teams would always include 2 people) This means that the appearance of Solomon, Bianca and Roisin in Week 10 is likely the whole of Team Summit by this point. We don't know whether there are 6 or 7 left at this point, but it seems a possible suggestion that Summit may lose Tasks 8 and 9, with James and Sanjay getting fired. An alternative is that Summit win Week 8 and one of James or Sanjay is ported over to Tenacity to level out the numbers for Week 9. Then if Summit lose Week 9 and the other member is fired, then that would leave Solomon, Bianca and Roisin as a team of three for Week 10. I think that whatever happens, its pretty likely that Summit lose Week 9. For now, though, we have no idea what happens to leftovers of Tenacity by Week 10, though I'd agree with Hown that Katie is likely still on board by then and Felipe, Mark and Daniel should all have some confidence of being on board by then (Considering one of them can only really get fired) James and Sanjay should be more worried as its virtually certain that one (and maybe both) are gone by Week 10.
I'm thinking something like (Week 4 to Week 7 is almost completely guesswork)
Week 3 - Lindsay (I think this is for definite given Karren's glaring "You should have contributed more" statement last week) and Nurun
Week 4 - (Jemma ported over to Summit) Steven and Sarah
Week 5 - Ella Jade and Lauren
Week 6 - (Sanjay ported over to Tenacity) Jemma
Week 7 - Pamela
Week 8 - (Sanjay and Mark swap teams) - Sanjay
Week 9 - James
Week 10
Tenacity
Katie
Felipe
Daniel
Mark
Summit
Solomon
Bianca
Roisin
This is largely guesswork for now and one of many ways it could go. Four double firings in a row (Week 2 to 5) is the main thing that irks me about the list.