What is the motivation for doing the change here, as opposed to doing the inverse change in downstream extension?

Second, if this is indeed the way to go, would it be feasible to expose the same identical value as both names? AIUI this is a pretty significant API-breakage and doing it this way would allow an easier and safer upgrade path for downstreams, where full deprecation can happen at a later point.

What is the motivation for doing the change here, as opposed to doing the inverse change in downstream extension?

Second, if this is indeed the way to go, would it be feasible to expose the same identical value as both names? AIUI this is a pretty significant API-breakage and doing it this way would allow an easier and safer upgrade path for downstreams, where full deprecation can happen at a later point.

Thanks for bringing that up, the decision was mainly motivated to mitigate risk as the extension is using rawTx and in comparison with mobile would it be just doing the migration and renaming in a few places on the other hand in the extension it would be a much bigger change.
I see your point of reducing even more risk by exposing both of the values as a first phase and only after doing the shift. I will bring that to the team.