I "get" the RX1 and X100s, there is a need for small, portable cameras with great IQ. The A7 and A7r I really don't get however. If you just want 30+ MP and/or greater DR than Canon offers, buy a D800(E). At least you will have a large selection of lenses available and know the manufacturer won't abandon you by moving on to a new lens mount or IBIS in a few months.
Not sure I want to get into this either but...for what it's worth...if a Canon shooter buys a D800(E), you can't use your Canon glass on it, which of course will normally mean a large investment in new glass. However, there's a selection of existing adapters that fit on the A7 & A7r. There are many videos of people already using Canon, Nikon, Leica, etc. mount lenses on the A7, so with the adapter, you can immediately use your Canon (or other) glass.
Plus, so many people here have said there's not much difference in 36mp vs. 22mp of the D800 vs. 5DmkIII, largely because Canon's lenses, in general
are better at resolving detail. I'm curious to see what that Canon's superior glass can do with that sensor. Of course, using an adapter could nullify any IQ benefit from better glass, time will tell. EDIT - Also, in Australia I believe they're giving away one adapter of choice with these cameras, and there's speculation other places may follow.
However, I do agree with you about being concerned about Sony's history of dropping products and moving on to something else. If this thing sells well though, Sony is more likely to continue to support it.