Originally Posted by Firegazer:
“The Master and Davros in the same series would feel cramped and OTT. Luckily it's just a rumour.”
Series 8 featured The Master, Cybermen, the returning Paternoster Gang and the Daleks.
Series 7 featured the return of the Daleks, the Weeping Angels, the Great Intelligence, the Ice Warriors, the Cybermen, the Paternoster Gang several times and the Eye of Harmony. Not to mention River Song appearances, and references to both the Silurians (Dinosaurs on a Spaceship) and the Zygons (The Power of Three).
I've not been keen on a Davros return until now, but I think it would fit in here. Series 2 did Daleks and the Cybermen simultaneously so The Master and Davros could work as well...just in my opinion

By including Davros and Missy early on I'd then hope that frees up the finale for something different for once, and also allows us to have a few Daleks appear early on to eliminate the need for a Dalek story later on, and also means that Missy isn't given centre stage so soon again (I like the character, but would love a different main threat).