I'm currently running 13th Age online through Maptool and Skype. As I recall, you're familiar with 13th Age so you know it tends to be, at least by the standards of the D&D-sphere, relatively transparent about a lot of opponent information, in part because without some of it, making decisions about talent, power and spell use can be basically an almost meaningless decision. So people tend to know things like hit points and some other odds and ends normally.
I'd decided a while back I was going to use dice roll macros for the last couple games I ran. This means that what I'm generating is quite visible to players, and in practice they can at least see the attack bonus of the opponent too.
I have found this surprisingly freeing. I don't even try to do on-the-fly fudging any more; if I mess something up, I tell them and we just fix it. I may conceal some things in set-up, but once the dice are flying, everyone sees about 95% of what's going on, and I don't miss being able to finesse that at all.