I don’t understand how leaving Thailand without canceling your extension of stay can harm you. You can’t be on overstay if you are not in the country. It would effectively be cancelled when you leave.
The work permit needs to be cancelled though. I did this a long time ago and they punched three holes in it.
I see a lot answers here are very involved, but I have a simple solution. Since you plan on coming "in a year or two," just fly over for a short stint and open an account so you can start sending 40k+ into it every month. Then by the time you're ready for your move you'll already have a year of transfers to show.
It can be hit or miss opening an account on a visa waiver stamp, but with enough effort you should be able to do it. The you can return to Aus or whatever you want to do.
can the transfers originate from your own account abroad? Can they originate from different accounts each month as long they are over 40k each and every month?
Will small transfers via Transferwise that add up to more than 40,000 baht per month count for this or does it have to be all at once and be “coded” as a foreign deposit, or something?