MMO gear based class changing

I was flipping through the October 09 issue of PC Gamer this morning and came upon the article about Star Trek Online. If I'm reading correctly, STO doesn't have set classes but instead your classes are determined by the gear you pick up along the way.  I've played two mmo's in my lifetime, one called Rappelz from which I was a champion (tank) and World of Warcraft where I tried out most classes but ultimately ended up as a Mage (Damage).  Both mmo's you started as a class and unless you paid ($25 in Rappelz, coming soon in WoW) you were that class from beginning to end.

Is this gear based class environment a better solution?  It could very well be, at least in my opinion.  Envision a dungeon party where your tank flakes out. In WoW one of the hybrid classes could switch to tank if they're prepared for it.  But at least in my experiences (I've never spent extensive time at the highest level) you usually end up searching for a new tank.  In this scenario really any of the 5 people (8 in rappelz) could switch to tank if they're carrying the gear for it.  And you'd no longer have to create multiple characters to accomodate for all the classes you may play within your guild, you could keep all of your achievements and experience on one character from beginning to end.  No more leveling another character to 15 seeing if you like it, realizing you don't really and switching... you could pick up a weapon, think "wow I really like the way this works" and start preparing for a character that could use the weapon with the most effectiveness.

Those of you more experienced in MMO's you think going this direction in future MMO's would be good or bad? and why?