I am eagerly awaiting the release of the game, and more importantly, looking forward to Ubisoft staying true to their words around the game being RPG-heavy, having good optimization for PC, having a refined combat system reminiscent of The Witcher 3 (which I loved), amongst other changes.
Knowing that the game is going to be huge requiring heavy time investment, I can see only one option for your case. And that would be accommodating both games in your schedule. Like playing one every other day perhaps?
EDIT: I am slightly concerned about the potential reduction in scope to the climbing aspect as well. However, as long as there are massive forts, several villages to explore along with mountains and pyramids, I think there will be frequent “rooftop” navigation sections.
I am more worried about the new combat system going by the game-play videos out there. The new combat looks very fast paced, with enemies attacking relentlessly from all directions and angles. I hope it’s not very difficult to master.