For me it's a toss up between user experience and more features and apps.
The biggest downfall right now for my site, is the fact that we don't have instant messenger (which I know was just released, but my site has issues with the recent update and we are trying to figure out why). Push notifications on mobile would also be nice for the messenger or at least something that lets the user know they have a message on their mobile.
Also the fact that there isn't an mobile app for our site is a big kicker...I took a poll on our site and the majority of people use their phones to access it.
The only problem with that is that even though UNA is responsive...people literally don't like to open up their browsers and have to go to the site...(Lazy yes, but that's where we're at now in the mobile world).
People want instant any more (aka one click) and that's another major factor holding our site back. Unfortunately, I've seen dolphins app for mobile and I wasn't impressed with it at all. <- So please don't emulate that with an app...
I have someone who is willing to build one for our site but wanted to see what lies ahead for UNA and that availability...?
Also, live feed would definitely be a good addition...everyone is on that kick now...
I know all this is slowly growing but those are the things that really slow any type of activity on the site...
In short, what I'm saying is, it's great if you just access if from a computer...not so great in the mobile world...