Assuming there's no scamdemic similar to Covid between now and 2030, you can continue to exit the country every 90 days without a reporting requirement.
Yes. Even now, most land borders require a TM6 to be filled out on paper. If it becomes mandatory to do one online on May 1, then unfortunately, even air arrivals will be affected. In fact, I suspect like Cambodia, they'll implement the online TM6 requirement for air arrivals first then for land ones later.
They won't ask you about 90 day reporting at airports or land border crossings, but they will put a 90 day reporting slip reminder into your passport.
It doesn't matter to immigration at the border whether you've done it or not, as they don't handle these matters.
A different story in China - or Beijing at least. Anyone who doesn't register their accommodation with the authorities (similar to the TM30) may get denied entry on their next re-entry and is ineligible for the 7 day visa waiver for transit passengers traveling via China, en-route to 3rd countries.