Why do it? For the look. For instance, I get different looks on Audi silver if I precede my LSP with AIO or MP (or any other "penultimate product"). It *is* sorta sublte and a matter of personal preference of course. FWIW, my favorite look on this paint is 1Z MP topped with UPP. With the proper prep, it's the best I've *ever* got this paint (just IMO of course).
I had minor bonding issues with consumer MP (the pink stuff) topped with UPP v2.0. Nothing major, just had to *really* let it set up and buff buff buff.
No problems at all using Pro MP (the stuff in the 1 liter can, less wax, slightly more abrasives) and the current version of UPP.
Haven't tried the exact combo of pink MP and current UPP but I'd expect it to work fine. Same ol' same ol' - try a small area and make sure it works. If it doesn't, it'll be like the UPP is just smearing around on top of the MP instead of setting up properly.
Can't really say about the durability as I only use UPP on the pampered S8 and I reapply when the slickness starts to drop off (yeah, I know, I probably oughta use the UGE instead..). Sure doesn't seem bad though. It's not like you just wash off the UPP or anything (even with that combo that had minor issues).