I seem to be experiencing problems with these of late, I haven't PvP'd much in a while and I recently decided to get back into it so the nameplates were re-enabled and I thought I was ready to go however the enemy casting bar at the name plates only seems to show for my current target while in times past it would show for all targets with a nameplate above their head making for easy fast interuptions combined with mouse over macros.
I thought it may have been an Aloft problem but I completely got rid of that and the default UI still gives me this problem. I was wondering if anyone could help me resolve this. Seems no point to having casting bars on the nameplates if you can't see every cast around you and only your targets.
Hm, the only reliable way I know of to get a non-targeted opponent's castbar is either Proximo (arenas only) or using focus frame, which sadly only works for one extra target. If anyone knows an addon that could show castbars for more opponents (say, within a 40 yd radius?) please do tell.
To avoid that problem there're two good addon: SpellAlerter and WitchHunt. They show in the middle of your screen what spell is casted by your opponents, both mod have a good customization however they really aren't a castbar.
as omglazor said Proximo can show you the castbar of the other team, but personally i don't like it (great arena frame, but nothing more ).