They've been working on the Apple Watch app, other than that I think Trello is pretty feature complete. What other features do you think they need to add?
One deal-breaker for me at least is the lack of id numbers on the cards. It's much easier to tell someone, hey I completed card #8 than "Really long description of task". I know there is a bookmarklet out there that surfaces the hidden numbers, but getting an entire team of non-technical people to run it consistently is near impossible. It really should just be a configuration option.
Also I've been requesting a simple list item count for at least a year. As in, show me that a certain board has X number of cards in it. Pretty basic stuff that is still missing despite paying for the service and asking for it multiple times.