Well, no. {xxx}, like {zo'e}, picks something that go in a particular place in particular predicate, this time the salient possibility, not just one that makes the bridi true. The {poi} clause provides, as always, the relevant predicate place. The plan, of course, is not really to introduce a new term, but rectify the definition of {zo'e}.
The rest seem fairly wormrunnerish. What purpose do you have inm mind that requires a shift of quantifiers to prenex? Why can't They be pulled it of sumti tails (whatever they may be)?
The underlying structure of {lo manta be re da} is lx2yMxy.
Insofar as that is not reflected in Lojban-- which doesn't seem very far, Lojban has moved away from logic.
Now, what theological situation is in terms of pulling that quantifier out of the tem and up to the propositional level needs to be worked out in the logic and might well also need some rules in the grammar, but that doesn't seem to be what you are about, since you stay at the level of terms but give ever farther from the simple form.