1: hide your IP (moot point if you're hosting your own bounce though. And a lot of IRC networks hide your IP for you anyway)
2: offer a way of keeping your history
3: store your unread messages server side.
4: keep all your clients and states synchronised
I'm not saying there's anything wrong with a web client (in fact I'm tempted to try the one submitted here). But I think there's a lot of misconceptions about bounces too.
In an ideal world I'd use both; have a web client connect to ZNC. So I can log onto the IRC client when a guest on someone's PC (eg cybercafe) but also have the ability to use native clients from the same nick for when I'm sat on my own laptop or on my phone (there's some half decent native Android IRC clients)
(Sync from WeeChat to Glowing Bear and between multiple instances is something we're working towards with the developer of WeeChat)
I don't want to run my bounce in a detached screen session, I want a proper daemon. It's easier to install and manage if it's a proper daemon. And if I'm going to be using a terminal based IRC client (which I often do) then I'd be running Irssi.
I don't want your stupid halfway solution when I already have a proper IRC bounce set up that does all that and more.