Used to like riding fixed gear for it's ease of maintenance and simplicity. If I was fit enough and riding everyday, it's probably what I'd revert back to.
Well, if I could get one with disk brakes. There are a few around with disk brakes and eccentric bottom brackets.
Honestly, I think disk brakes are the biggest single advancement in road cycling for non-pro-athletes. That, and sensible cleats. The rest - it needs to just work and be easy to maintain. I rode a bike with friction shifters on the down tube for a couple of seasons. You can get used to that. It's fine. Crap brakes ... that's unbearable.
And anything that needs an app ... well that's just annoying. The smart phone has just become a key part of the cycling eco-system. Speaking as an IT person, that's going to cause some people pain one day. Still didn't stop me buying a Di2 equipped bike though, did it? The electronic shifting is glorious. At least for now.