Problem with the D'deridex is pretty much the problem with a lot of fed cruisers.
Cruisers generally rely on shield and hull tanking. To make them viable at DPS, one must be lost. Now for PvE this isn't a problem but for PvP this will geneally mean you're cannon fodder for escorts. The upcoming changes to emergency power to shields is going to make this quite an issue for cruisers, since they'll have large drop in shield resistance and regen for 5 seconds, which is more than enough time for an escort or an alpha-striking bird of prey.
Escorts and sci-ships on the other hand are less reliant on emergency power to shields, with some being able to hull, shield and speed tank.
This all basically compounds the D'deridex's problems and makes it solely desirable for RP or an Romulan engineer who wants a healer build.
Personally I'm holding out for a Mogai, even though the D'Deridex is the ship I like the most aesthetically.