It seems to me that an alternative could be to simply pair FUSE with any standard file explorer.
If they think they can make a better file manager, great, go ahead. But including transports in the file manager means that remote data only looks integrated, it isn't actually available to local apps.
Or (just as bad) they'll decide they need a copy-to-local and copy-back-to-network mechanism, which will work for some files opened by some apps but not all. Arghh.
Nemo (under Linux) does that for some protocols (eg. Android media transfer), and it is very annoying, especially as there are already FUSE drivers for (at least some) such protocols. In practice it means that the only thing you can do using Nemo is copy/move files around.
I am not convinced file managers need to be cross platform. There are plenty that will run on any desktop, IMO mobile platforms need different functionality and a very UI.
The real product as described on their website (not the github repo the linked) is that it is a drop box like sync service integrated into a file manager. I think most non-geeks will find it confusing compared to something that integrates with the familiar OS default file manager.
https://github.com/osxfuse/osxfuse/wiki/List-of-macFUSE-File...