wow, you guys can mess things up. Don't mind people that spent 5-10 years building and supporting software around you. Your regular releases cause enough headaches. Normal companies do backward compatibility for APIs, have you heard about things like that?
I'm not sure what you think we've messed up; here's some further context, to better understand our forthcoming changes.
The last breaking change to PPro integration was 11 years ago, in 2012; we replaced Flex panels with CEP + ExtendScript integration. We supported both integration methods for ~1.5 years, before discontinuing support for Flex panels.
For the past 11 years, we've improved and expanded the functionality available via CEP + ExtendScript...without breaking backward compatibility. So yes, we have heard about things like that.
Like other Adobe point products, PPro is replacing CEP + ExtendScript integration, wherein the UI is handled by JavaScript of a web page being loaded in a Chromium instance and host interactions are handled by ExtendScript, with UXP integration, wherein all interactions are handled via modern JavaScript.
I answered "Yes" to your question, because there is no way Adobe can make existing integrations work under UXP without modification; existing integrations will need to be rewritten.
While we work to make UXP integration available, we are no longer implementing additional ExtendScript APIs; any new requests (like yours, to provide an API to manipulate media placeholders within .mogrts) will be delayed, until UXP integration is available.