I can confirm this as well, currently residing in California.
I am a LEP.
I had the game installed through Steam; No Horizon choice anymore today at 8 am local time.
I tried installing the regular launcher and logged in: No Horizon anymore today at 8:15 am local time.
My orders are a mishmash. Bought Elite Dangerous Mercenary Edition from Frontier store. Later on I claim my steam key and bought Horizons from Steam. All my paint jobs are bought straight from the Frontier store.
Horizons still works for me, I am still allowed to buy paint jobs directly through the Frontier store and do I have go through Steam store now?
Must affect the steam account then? I'm also an LEP owner, the launcher update went flawlessly as far as I could see from a brief logging in. I don't have a steam account for ED. A mistake that I often make (but I doubt it has anything to do with the issues here) is that I usually pull a link of the launcher into the taskbar. Then I forget to do this again after an update as this link (in the taskbar) will be broken then.