I'm on Affinity Designer Beta for Windows, and I must say I'm blown away by how good it is, but lack of separated font folder is a deal breaker for me. Installing all your fonts (around 4000 in my case) into a system is really "no go" on Windows OS.
Reasons:
Lot slower boot-up time
Bloated operating system
Unnecessary memory usage
Some other applications are loading all the unnecessary fonts for them that way....
It would be great if you could create separate folder somewhere in the Affinity directory for the fonts that will be used only with Affinity applications. Adobe has it, you should definitely have it.