Just a guess, chances of new WM1A in 2020 is 0%, 2021 is 10-15%, 2022 is 15%-20%. Well, you get the gist of it...
Realistically, I think with the world economy going down the drain now, maybe 2023, and given how slow Sony does things, more realistically maybe 2024 or 2025, if we are talking about WM1XXX successors. And besides, modded 1A/1Z is just so ahead that it would take huge discoveries and implementation on Sony part to comfortably come with worthy successors.
Put it this way, it makes more sense for the world to discover vaccine or cure to Covid19 much earlier than Sony to come out with successor to 1A/1Z