As far as I understand, Fil-C changes the ABI of the system, therefore it requires a new architecture in Debian terminology, e.g. amd64fil. And then you'd need to use multi-arch to pull in amd64fil binaries where that works.
We'll have to see how this plays out but it's not super plug and play.
Exactly something like that, yeah.
Some notes about that here: https://cr.yp.to/2025/fil-c.html