Paul hasn't committed to details on the next T4 follow on unit yet - at least in his last post on the subject. It is one possible direction that seemed noted as likely. But one candidate MCU isn't released from NDA yet - and once suggested he may go another direction first …
The tiny Teensy 4.0 was chosen because it would be easy to knock it out - maybe not even a full two years it seems to release … though the 1062 MCU was only shipping in quantity partway through the beta allowing change from 1052.