Dear Richard,
When it comes to metering, I really suspect that "can't" is the right word. My understanding of SLR meters is that the cells are in the diverted light path, and as there is no diverted light path in an RF camera, there is nowhere to put the cells. The only possibilities in an RF are therefore reading the light reflected from the shutter (the universal approach today) or the lollipop-on-a-stick of the M5, which is about as 'spot' as an SLR 'spot'.
Power consumption is almost certainly a matter of time when it comes to battery capacity, but heat dissipation from powerful processors is a non-trivial matter and likely to remain so for quite a while, I suspect.
The smaller DSLRs are not, as far as I am aware, 24x36mm and I fear that the bulk of the components will render it difficult to the point of impossible to incorporate moving-sensor IS in an M9-size body for a very long time, possibly forever. For processor-based IS, we're back to heat and battery life.
Point fully taken about seals being more against dust, etc., than rainstorms (as with 'waterproof' watches) but I've hardly 'babied' my M8, which I've had since shortly after it came out, and it's not been a problem. The Great Internet Whinge, often from people with no experience whatsoever of whatever they are talking about, magnifies all problems beyond belief. This is not to say that problems never exist, but if Leicas were as bad as some on the internet say, they'd never sell more than one camera per person.
Finally, I don't think anyone ever said a digital RF was impossible for all time, just that it was a damn' sight more difficult than most people seemed to think, especially the ones who didn't understand lens-to-sensor requirements. Leica themselves said they'd do a 24x36 sensor eventually, but that they didn't know when.
Cheers,
R.