FDW are a great way to access external data sources, but it lacks proper support for visibility and transactions, and so on. Also, the FDW API follows the "tuple at a time" execution model, which prevents a lot of optimizations in the upper part of the stact (vectorized execution etc.).

There are several products using FDWs to change storage, but I'd call it a misuse of a feature designed for very different purpose.

IMHO it's hardly a way forward without significant changes/improvements (which may happen, I don't know).