[Seymour]

The user interface is very, very awkward by today's standards,

I so completely don't care ;-) Call it quirky but I mainly shoot in manual mode. All I ever wanted in the way of 'interface' was a dial for the aperture and a dial for the shutter. And a decent viewfinder <sigh> I hate a camera that tries to be smarter than me or read my mind or something. (Maybe except if it's a compact.) I don't want it to be my personal assistant - I want it to be my personal image taking slave. Carry out my orders, to the letter, and not ask any questions.

Granted, the whole auto ISO thing sounds promising but mainly, I find things like matrix metering and scene modes useless, distracting black boxes. Much too much effort trying to remember what they do exactly when it is so easy to remember what the basic image parameters do.
 

6mp sensor rather limiting in resolution and noise above ISO 200.

And yet, in 2003, its high ISO performance and resolution was sufficient to make me give up pushing Kodak Tmax to ISO 3200 ;-) Took a lot of nice pictures with it despite these shortcomings. Sufficient sensor quality for most of what I do is a given in any system these days.
 

No idea why you would want to go get a MFT or Sony mirrorless and expensive metabones adapters, and go Canon lenses.

That is easily explained.

I finally want a decent (and of course 100%) viewfinder to work with again.

It is the single most important piece of "user interface" after all. https://luminous-landscape.com/understan...ewfinders/

I find the established brands, and especially Canon, have become complacent and lazy, their DSLR bodies overpriced, underperforming and putting unwarranted restrictions on my creativity.

I need to wear eyeglasses, which I find impractical to remove for shooting (as well as for using binoculars), and Canon viewfinders have consistently underwhelmed me regarding coverage, eye relief and the option to put in different screens. When they cancelled that option on the 5D MkIII, I lost the last remaining vestiges of interest in Canon bodies. The future is mirrorless, configurable, and adaptable.

What I do care about though, among other things, is build and image quality, which is why I like a lot of Canon lenses.

Another thing I do like is the genuine Canon USM with FTM. If you do have to have AF (see below), that is the nicest implementation I have tried so far, as soon as you can transfer the AF start away from the half shutter press and to some other discrete button where it does not get in the way.
 

Any Canon DSLR will have waaaay better AF performance than the old 10D you have.

Another thing that I could not care less about ;-) For the things I shoot, I find autofocus to be highly overrated. I'd take a system optimised for manual focus any day of the week over one that is covered in 99 AF sensors but does not give me decent manual focus control.
 

You still have to check results.

That goes without saying ;-)