With the upcoming addition of transmogrification, I was thinking of how this could improve the “City sitting†syndrome that seems to plague our beloved game. Obviously, people will be traveling to older dungeons and raids to acquire long-lost sets of armor for vainity's sake. I know of a few people personally who have resubscribed to find those sets they had once upon a time.
The potential for getting people to resubscribe- and stay subscribed- could be much greater than the simple gathering of one or two sets that have been out for years. What if Blizzard offered "Limited Edition" armor sets/pieces.
For example:
"This month in Azeroth, travel across the dunes of Tanaris, and seek out the mysteries of Uldum! For a limited time the <Desert Wanderer's> set is available! Grab it before the secrets needed to craft it are gone...forever!"
Said event would last one (or more/less) month, and the "set", whether one or eight pieces of gear would be unique in the game for the time it was available. Then, the next month/period, a new set would be released. Obviously one would prefer if seperate sets were made for each armor-type, but I suppose they could all look the same.
Thematic armors will become popular, and many people would probably try to do something of the "desert armor" or "tundra traveler" type things anyway, why not make it a reason to subscribe, and more importantly, leave the cities?
The methods for attaining said armor could be many: quests, dailies, pvp objectives?
Another idea:
Holiday armor: sets that are available only during a particular season and year. For example, one year the Halloween set could be pumpkin themed, the next year bat themed, etc.
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And of course, those lost sets/removed armor. While many will be clamoring to bring them back, maybe instead Blizzard could decide to release them in recolors through questlines, dailies, etc. That way those who have held on to them all these years still feel special, and those that just like them for the looks can have them too- in a limited capacity.
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Eventually, we'll all be a little more unique thanks to Transmogrification. Why not take it a step further and make it another reason we subscribe each month?