A short term memory is an acceptable substitute for trust

Honestly, a u-turn is not enough because of the broken trust. They'd need to cut off their (perceived or real) ability to "change the deal" like this again. Like make it clear you get a perpetual license to distribute the unity runtime for products produced while using a validly licensed unity editor. Make it so the customer has to take some affirmative action (not just clickthrough a generic new version TOS screen) to upgrade to any new TOS version which removes that license.