Was able to log in after a combination of validating game files, and then flipping back and forth on the selector between Elite basic and Elite Horizons. I don't know if any of that was actually helping or if I just hit something random but eventually the blue "Play" button came on and I got as far as the "Ship Bay" screen showing your current ship in the starport. (Mind you - the server status on the launcher still said "Issues detected")
I noticed then that Arx update had failed.
Hmm... Best not push my luck. I could wind up playing for a couple of hours and then have my progress reset or something.
Decided to back out and shut down. I'm satisfied there's nothing wrong on my end or with my game files. So it's just a waiting game to see how soon Frontier can get things fixed on their end. I've read the thread and spotted the Dev response. So at least it's not a case of "It's the weekend, so see you all on Monday!". They're aware and somebody must be working on it.