Strangely, R/D/R is probably the second most likely scenario overall and the likeliest if Trump loses in 2020. D/D/D is insane and the only I can see R/R/R happening is if Trump just barely loses. Given where the states are moving, the 2022 map is almost as bad for R's as the 2018 map is for D's
What if Trump is unpopular and one or two Republicans become Democrats, perhaps John McCain and/or former Blue Dog Democrat John Kennedy (if he wins in LA). I can only see R/R/R if Trump is popular. R/R/D barring party switches by Senators. With one or two Senators changing parties, R/D/D maybe.