No, I'm not evading your point at all. The stuff like WU/Avast/godknows what caching was already there. It was removed because it was BROKEN. If it works for you, add it manually and move on, It didn't work for vast majority of users, worse, it broke other things, noone has time to maintain similar things. Squid is NOT the way to distribute Windows updates. Even if you can use every tool as a hammer, it's just not a good idea.
Just to be crystal clear about this, look at
https://redmine.pfsense.org/issues/3847
http://wiki.squid-cache.org/ConfigExamples/DynamicContent/YouTube#Discussion
So yeah, it just doesn't work any more. Then there was Avast – they've switched to streaming updates ages ago. Nothing to cache there, dead code. Symantec - ditto. The only thing that might possibly be working is the Avira stuff, but that's just due to the fact that their AV is very much dead and has not moved anywhere for past 10 years or so, except for inventing more and more aggressive ways of nagging users with fullscreen advertising pop-ups. Why should a pfSense package care about someone using a dead AV?
When you have barely 1 person to occasionally maintain the code, you just do not add bloat well known to break every couple of months to the code. And if it's already there, you remove it.