This is more in line with what I was picturing, except I didn't really think of Confessors getting there. They could though. That'd be pretty terrifying. That said... I agree with this sentiment, actually. I want stealth - I think stealth mechanics are very important. But it shouldn't just be complete invisibility. I'm not sure what the best approach is, but I hope that it's more interesting and complex than that.
I don't think this idea warrants an entire archetype, but it might make for a great promotion class - perhaps for the frostweaver? It's an idea I've always been in love with but have never seen in an MMO before. I've kind of pulled it off in single player RPG's like the TES games (usually with mods, the vanilla games don't support it well). It just seems like a great idea for more class diversity. I'm hopeful that there will be a decent amount of variety in every role, and a stealth mage could be another option for infiltrators and scouts.