Is a 10 inch big enough to see everything and be comfortable hitting links (no stylus)? Or do we really need to think about a 12-13 inch screen?
I’m running a Nexus 9 which I believe is 8.9" It felt too small to start with but I have got used to it. As a remote this is a great size, I wouldn’t want anything much bigger.
I find it quite usable on a Nexus 10. Not feeling tempted to go larger.
I’m using a Surface Pro 3 as a “Remote” : 10.8" 1920 x 1080 LED
No problems or wishes to have a larger screen.
I’m using an 8 inch nvidia shield tablet. From a device purpose perspective (remote) it is perfect, but for Roon in its current Android incarnation i would say it is the minimum.
If you dont mind having a larger tablet then i would go for it. Personally though i love the 8 inch size better and like Roon just fine on it.
I have a Nexus 9 and think that, in spite of having my preferred aspect ratio of 4:3, it’s just a bit too small, not just for Roon, but also as a full size tablet. It’s kind of halfway between an Air and a Mini and, IMO, it fails to be either.
I did buy a 12.2" Samsung Galaxy Tab Pro (which I returned when I discovered a battery fault) which has a wonderful sized screen, but was big to hold. Further, I’m not sure if the Roon app is able to make use of all that real estate.
Rapidly coming to conclusion that Apple got it spot on with the size of the original iPad and its successors.
I can only echo the sentiments described above. I bought (and sold) the Nexus 9 and an 8 inch Sony Experia Z3 in rapid succession. I also learned that I really dislike Android. 
I’ll just sit tight for the iOS release and see what iPad works best by then.
“But me, I sit here so patiently, waiting to find out what price
I have to pay to get out of going through all these things twice…”
I have used it on a nexus 7 and its too small. Personally I dont think this is a tablet size issue per se, I think it is just inappropriate to directly port the desktop version to a small screen. It needs to be a specific small screen size appropriate version.
I also have an ipad mini, but I think its going to be too small on that too.