Is there a word/term for a "super-contraction"
Solution 1:
I was considering evolutionary or progressive or intensive contraction. However, these words have connotations of aiming for better, which does not seem to work in terms of contraction.
Then I would suggest degenerative contraction. I would also consider iterative or recursive contraction. These suggestions are far from being precise, but they might give you some inspiration.
Edit: Based on some wisdom from the comments, I would also call it over-contraction, since the contraction Ima or even I'm'a could make little sense to and confuse people.