This is what Anet had to say when asked if they would accept custom emblems for guilds:
In order to maintain absolute security for every element of the game, we are not able to accept externally designed submissions for inclusion into Guild Wars. However, we have already hosted one official Guild Emblem Contest, and we plan to hold such contests on a regular basis. The emblems that are created in such a competition become available for general use, rather than the use of any single guild. We encourage guilds to consider taking part in such contests if they wish to see their emblem as a possible choice in Guild Wars
So if they ever did accept any player designed armor and equpment, it would just as likely be available to everyone, and not just the guild that wanted it. Thus pretty much defeating the whole purpose of designing a set for your guild in the first place.