I'm not going to use such strong language as Warren, but I agree with him completely. People see the two parties in the U.S. and assume they're monolithic entities, forgetting that the parties themselves are coalitions of ideas. Democrats have their establishment group, their democratic socialists, the blue dogs, etc. Republicans have their establishment group, Trumpupblicans, liberty caucus republicans, etc. For the purpose of this proposal, those sub-factions are separate parties.
For example, part of the reason that Ron Paul retired when he did is that his party was planning on splitting his district out from under him. Regardless of your opinion of Dr Paul, that shows that those with redistricting authority will use that authority to not only make sure their team wins, but that the "right" people on their team win.