You have primaries only. Example: If Cruz wins 60% of the popular vote in a State Primary, he gets 60% delegates. At the Convention, the delegates are loyal to him for three rounds if he does not by the the first or second ballots. If he does not win by the third ballot then it is a free-for-all. If it is more complicated than than you only get approved “establishment” candidates. Cruz, unfortunately, has indebted himself to the GOP/Bush Family/SuperPACs and I consider him now to be part of the DC Cartel. Note, Primaries are not fodder for the Electoral College. The Electoral College is for the election of the POTUS only and gives smaller states equal representation. Primaries is for the election of the candidate to run for POTUS.
I like the full proportional idea, but what do you do with the drop outs? Do they become ‘unbound’?
If so, I think you would find that even in Florida the going would be tough for Trump.