> Architecting to make portability easier should absolutely be a thing.

It is, but it's really hard to make the right trade-offs. Usually I'd start by basically making a list of what could potentially be done to make it easier, check lightly how hard each one of those will be, then sit down with stakeholders and figure out the balance between how fast they want to move, and how risky they want the migration to be. Some opts for less safeguards and moving sooner, others for absolutely less risk but it takes the time it takes.