It wasn't a huge deal. BYOD update is just a USKP sync-up. So I was content to try and wait for this to blow over. Except it hasn't.
I've since spent the better part of the last 6 hours trying to unravel my network setup to see where this thing is breaking down. Windows Firewall got turned off. The firewall on my FIOS router was turned off. Still Steam returned with Error 35. My Google-fu has also failed me today, so I started whining about it in a chat room, naturally

Hanaisse found a few scattered recent posts on the Workshop from other modders who are also running into the cryptic Error 35. So it appears there may be some sort of underlying problem here.
I've been pretty much over all the basics. Firewall checks. Rebooted the router. Rebooted the PC, several times. Logged packets into and out of the router, and nothing stands out except for something that appears to indicate Verizon might be blocking the traffic, but I can't tell from my end. Besides, I can't think of a good reason why up until 3 days ago they'd have just let it fly and now suddenly it's blocked.
I'd have just let it slide even then until Monday when I could call them, but I'd like to get the USKP update out of beta now and that requires that Steam allow me to update it.
Has anyone else been having issues? A few isolated cries in the dark kind of confirm for me that this isn't just my system suddenly acting up.