I should have guessed it would be you :-)
I've been gone for a few months, and now back.
I'm just about to rent the darn A7R2 setup for 4-5 days.
I think $220 to try before I buy is totally worth it. Samy's wants $480 for the same setup/body and adapter to rent. All online rentals were at least half of Samy's.
Not many here do lux/jewelry product shooting, which I do, and its one of the critical subjects that need to hold all detail. I use the 22mpixel P25 now, so it would be a nice chunk larger file and detail. So would the 5DsR, and maybe a LeafAptus75(33mp) P40, or 45, all these in around the same range of price, maybe $1K-1.5K more($3000-5500). Considering that I don't change gear every 2 years, its not a big difference/I still use my 5Dm2!.
I was thinking about it when the first A7R came out, and then when Canon did the 5DsR, I also thought about it. I also use the 5Dm2 now with a good set of lenses(70-200L IS, 24-70L, 50/1.4, 100Macro, 180LMacro, Leica 100r, 60r)
The thing is, the P25 I use produces great files and I'm happy with it. 5Dm2 cannot come close. (My old Kodak ProSLR, 14mpixel(no AA filter, ccd) was much closer to the mf "look of 3D" we talk about, but it was horrible with controlling lights and color.)
Pros using A7r2 or 5DsR...vs a MF dB
1. I can always gain from more resolution,
2. My back screen is out, so its like my H25, and even when it is working, its not very useful.
3. Faster shooting and transfer would help a lot.
4. Portability would allow me to give it multiple purpose
Cons using a A7R2 or 5DsR...vs a MF dB
1. I don't know how large the subject will look on my Sinar. It was a bit odd with my Caon using slide adapter.
2. I can't use it on the Mamiza RZ kit I have. The kit is a complete one with all lenses, and I have not used it in a long time. Since I can't make use of the P25 or H25 on it for portability use. Tethering is OK, but more of a pain.
3. I like using C1 for tether capture, not sure how these will adapt.
4. I use Shneider and Rod HD macro glass. Not sure how the smaller pixel sizes will do with them.
5. slight learning curve to adapt to Sony (not a real con)
6. Not sure how meaty the file will be for post editing.
7. Lens distortions?