These sites rely on network effect, which become prominent after a certain threshold of users join the site. If they reach critical mass, they will suck in the rest of the extreme-right, then the republicans then slowly everyone, because people like controversy and will seek to go where they can have it.

Reddit is clearly a leftwing site now in ways that it wasnt when it started (when libertarian was the dominant ethos). All their "common word" reddits, such as news, politics, technology science are purely leftist echo chambers by now. The few rightwing corners left are already isolated and ready to make the move. In fact they may even decide they should jump ship. What better time for /r/t_d to go somewhere else than now, when people's interest is intensely focused in elections and they can easily rally all their users to follow them. Wherever they go, more people of other persuasions will follow, because people love telling other people that they are wrong on the internet.

The question is if those other competitors can stand the traffic and whether they give the features to moderators that reddit does.

Subreddits can be unwanted by Reddit, but otherwise non-toxic.