I've wanted sideways/vertical slabs and stairs for a long time! But apparently they'd have to completely re-do how slabs and stairs work to do it. I'd say it'd be worth it though! 22° vertical slopes need help!
I want more pet/animal interactions! Play fetch with dogs and sticks, give cats yarn balls to play with, give them a "wander" option so they don't have to stay in one spot all the time.
I haven't yet faced one in survival mode, so for all I know they might need some balancing, but overall I really like the design and idea of them. ^_^ The "lasers" thing does seem a bit odd, but again, I don't think it's game-breaking.