If the parks are resort guests only WDW can test everyone before check in once and leave it at that.
If you do not want to allow WDW to test you then you can get a refund and come back later.
To me this is the only way to get around the masks and have onsite transportation (still not MDE)
We will need a lot more test available before that's an option. Right now everybody with symptoms who thinks they might have it can't get tested. No way can test capacity be used for WDW/Universal/etc until that situation has changed.