On that note, I'd appreciate if someone who maintains PlayStation / Windows ports could cleanup standardsUserAgentForURL to use WebsitePolicies in WebKit layer instead of having the logic in WebCore.
Looks like standardUserAgentForURL is a stub for both PlayStation and Windows? Only the UserAgentGLib.cpp implementation of standardUserAgentForURL actually calls into UserAgentQuirks.cpp. What exactly are you hoping to have changed?
If anyone seriously looks into changing user agent quirks, it would be a good time to try investigating https://bugs.webkit.org/show_bug.cgi?id=191858 as well.