1. You "remember hearing" that dev restarted? Nintendo said it explicitly.
2. It will take 2-3 years minimum. It's a 2021 title at best. No one should have expected anything at e3. They told you it was restarted because it will be a long time. We won't see it until late 2020 at the earliest
3. Nintendo's last CEO, the one in charge when Switch launched, said they wanted switch to last longer than a normal console cycle, which is 5-6 years. So going by 2017, that means 2023. With node shrinks and such, I think 3 or 5nm, maybe stacked boards, etc will also help them wait until 2023-24 for next gen so I wouldn't worry about MP4 being put on next gen. Next gen is still 4-5 years away for Nintendo