For those of us who are only half paying attention, why is mirrorless an inevitable step?
I would have said that the advantage in sensor size of 35mm DSLRs would give them a long-lasting advantage over anything with a smaller sensor, even with advances in that technology.
They're also quieter (no mirror slap) and having an electronic viewfinder allows you to see what will be recorded. For example, you can directly see the effect of a longer exposure or higher sensitivity.
That's not because of the cameras being mirrorless; it's because (for Canon anyway) they purposely gimp video on their DSLRs to get you to buy their Cine-EOS cameras.
Strides which do not result from them being mirrorless.
You should understand that the mirror does not get involved at all when doing video with a DSLR.
So, all of these 'strides' can and have been replicated in the next version of the cameras.
I'm not sure what your point is - it's mirrorless that have really pushed the tech on here at least at the cheaper end of the market. It's my understanding that Lumix G range for example has been widely adopted for video in a way that SLR has not. Are you saying these users will defect to SLR with a new generation? Can't really see why, since all that going SLR would do is introduce some extra mechanics they don't need.
DSLR/Mirrorless is unrelated to sensor size. Sony makes 35mm mirrorless cameras with great sensors, just like more or less everyone making DSLRs also makes some with sensors smaller than 35mm size.
I would have said that the advantage in sensor size of 35mm DSLRs would give them a long-lasting advantage over anything with a smaller sensor, even with advances in that technology.