i don't think anything can digest/ferment sucralose. it's pretty indestructible. i suspect you're stuck with it, and its taste.
will the beer taste any better with the addition of sour? throwing in bugs might add some sour, but the sweetness will remains (hello, Lindemanns...)
the conventional wisdom is that souring a bad base beer will not yield a good result. i'm don't always support that position, you can take some less than stellar beers and make them really good. but one that is flat-out undrinkable will have next to no chance of being saved by bugs. if you have the space, aging vessel and the patience, go for it... but if you want a decent beer, you'd be better off making an all-extract batch and souring that. if you're going to wait months and months for a result why risk starting with something that likely won't work?
