I'd like to see EQ2's player housing system in any other MMO, but especially in place of the pathetic housing system in LoTRO.

It's many years since I dabbled with AC, but one feature from that game that I'd like to see in other MMOs is the frequent caves and dungeons that you could just stumble across at any time. They would fit well with the open world of Vanguard, or even EQ2, where there is a theory on the part of the developers that such places should be few in number and group-only in content.

Which takes me on to my final desired pairing - the outdoor world of MMOs such as the ones I've already mentioned with the extensive dungeon content of DDO.