BYO routers have been A Thing in a lot of countries. I haven't worked for an ISP for nearly 20 years, and they were very common even back then. With the demarcation being provision of service it's extremely easy to see them as online in RADIUS and anything past that is not your problem - anything past the primary entry point is the customer's concern, same as any other utility.

If you have equipment that's not authing, that's a slightly different kettle of fish - usually involves basic troubleshooting but if there's a seriously farked router or the end user can't even log into the unit then the responsibility doesn't lie with the ISP. It never does with a BYO.

The EU isn't going to go crazy monkeypants with this shit, that's ridiculous fearmongering. They're simply stating that ISPs can't force customers to proprietary hardware.

Advertised speed cannot be reasonably interpreted to include consumer-side routing, that's like thinking a car's advertised top speed applies regardless of local traffic regulations. Add an asterisk and the smallprint "with an ISP-provided or equivalent bridge directly connected to a single sufficiently fast client device".

Also, if ISPs actually provided a proper bridge people would not be using their own stuff. Practically speaking the issue is not some watts of power but getting rid of routing layers and being able to see (not necessarily control) some information about the fibre link. I'm pretty sure if ISPs asked nicely mikrotik would build them a thing with an sfp and a 10g copper port on different sides of the box with some empty space to throw some fibre windings in, mount it to the wall covering the incoming hole, supply power, connect anything via pppoe (or maybe it's time for a successor).

Actually that was how my first dsl ISP supplied things: A modem and a router. You could toss the router, connect the modem to a switch, and even have five simultaneous pppoe sessions. And I don't think even non tech savvy customers are all that hell-bent on AIO devices given that you might not want your AP to sit in a cellar with bad reception.

...actually, that's not even dissimilar to how things are in power distribution: Over here you have the house connection, a beefy thing with melt fuse and power meter, out of which comes three-phase to the actual distribution box. Ordinary electricians aren't allowed to touch the thing with the power meter, they need an agreement with the network operator to handle that stuff. Which is kinda important because not every operator's infrastructure looks the same, grounding requirements might differ etc. it's a whole can of worms.

On a different note: It might be a good idea for ISPs to switch to advertising link and upstream speed separately. It's not like they're going to provision for a gazillion gigabit links going full tilt at the same time, anyway, but you can provision for a minimum guaranteed speed and allow line speed when sufficiently many other customers aren't using upstream. "Fast if the roads are free and we guarantee traffic jams no slower than X".