Wanted: electronically switchable crossover / changeover switch

As big as the fear of smart seems to be, I would recommend a classic installation.

Maybe I have found my combo: impulse relays (ELTAKOS). To this proven technology (?) I can add more virtual (i.e. microcontroller-controlled) switches at any later time. Some Eltakos also report the current status back, so it can be queried at any time. Each room gets its own Eltako, an Ethernet cable is proactively run to the junction box, and at a later time a "smart" switch can be added there.

Or: the Eltakos are mounted on the DIN rail. However, then every single room light and every light switch would have to be pulled all the way to the fuse box.

Is the consideration correct?
Does it make sense?
Has anyone done that?

If you put everything in the cabinet, you're basically prepared for almost everything that will come. The copper price is going up again a bit after it dropped significantly. I would calculate how much extra cost that means. Basically, I think the idea is good and would do it that way. But for me, it's too uneconomical.

Please do not put the Eltakos in the junction box. That's just Fred Flintstone. You won't save anything anyway if you also install Ethernet cables.

Isn't it more sensible to install a few motion detectors in transit areas like the hallway?

More sensible than what? Motion detectors are probably quite useful, maybe also in additional rooms. Or even in all of them.

I would also rely on Shellies here. Yes, if the electronics of the Shelly break, the light will no longer work. If the electronics of your impulse relay break, the same thing happens. However, you can replace the Shellies yourself, and they have been running reliably for years with me. By the way, local switching using a button/switch also works if you should have WLAN connection problems. Remote control via app (cloud) or Home Assistant then no longer works.

As a small solution, I would take Shelly. If you want it done properly, then KNX with star wiring and corresponding costs.