I doubt that any Apple desktop will ever be "powered" over a USBc connection.
Simply not enough power.
If they're going to go for an external power supply then it would be dumb
not to use USB-C - even if it didn't mean that you could use a harden variety laptop brick.
The 150W and 180W power supplies in the current M2 and M2 Pro are well within the current maximum 240W supported by USB-C/TB power delivery - and represent a pretty generous safety margin over the actual 7 to 50W power consumption that people report - and the M4 is supposed to be significantly more power efficient. I think a big part of the consumption is the need to potentially supply 15W to each downstream TB4 port, also, without a battery, it has to be able to cope with any spikes...
The Apple Studio Display can supply 96W, and making the new mini Mac mini work from a Studio display would be a good target... you probably wouldn't notice a Mini being throttled to 96W.
There's no advantage to using a 'break-away' magnetic connector on a desktop - with no battery you really don't want the cable to pull out accidentally and crash the machine, and the "let's play power-brick Twister' scenarios you get with laptops shouldn't happen with a desktop. The iMac design probably pre-dated 240W USB-C power & they made the thing too thin for an internal PSU or Ethernet jack.
As for Ethernet in the power brick... Well, that's what happens when the designer is living in a bubble (or, more likely, an earthbound flying saucer) where the ethernet sockets are
always on the wall right next to the mains sockets, and never stops to think that might not be true for everybody...
