Had a 16t quad adapter on my first mountain bike
Not that it's of any relevance here, of course...
When I got my first MB, almost 20 years ago, I was way too fat and slow to ride in the mountains where I live. It came with a 30t small ring, and I was so newbie I didn't even realize you could change that. I spent $29.95 for a Quad Adapter that required removing the crankarm (didn't know how, didn't have the tools), taking off the small ring (didn't own an allen wrench, but at least that's the point where I realized, "Hey, I could just put on a smaller one of these for about three bucks"), mounting an adapter in its place, bolting the small ring back on top of it, then putting the 16t ring on the adapter and reinstalling the crankarm.
It went together OK, considering my skill level. But I never could get it to shift right--any time I wanted the granny, I had to reach down with either my foot or my hand and nudge the chain over. I could have ridden up the Washington Monument, though.
As for the triple one, I haven't seen them, but it doesn't sound like it would be hard to design. As somebody else mentioned, BB spindle length may be an issue, and your present front derailleur might not shift a triple, though most will.