Hating on Latinos and Muslims continues to be a winning strategy, so I expect we'll see more candidates with even more outlandish proposals in that regard in the future.
I think he means in terms of the process itself rather than what candidates propose.
The problem with proportional systems (and I'm not sure when the Democrats enacted theirs) is that they tend to lead to consistent contested conventions. And considering how divorced delegate selection is from voting in the Republican Party, that could lead to results much weirder than
trump being shafted for Cruz (Paul suddenly becomes a viable candidate in both '12 and '08, for instance).
So, we maybe see greater proportionality early in the process, but I think that would have to be counterbalanced by making the end of the process
all WTM or WTA (which it already is, so
maintaining might be a better word).
One thing we might see is pressure on state parties to put in very low or nonexistent thresholds --
trump built up his lead not from overwhelming victories or even from WTA, but from opponents not making thresholds due to backfirings of strategic voting. The problem with this is of course that some delegates will end up pledged to random nutjobs who run and get 1-2%, but that's preferable to someone like
trump coming in.