There is a balance between building up muscle, and exercising so much that you end up with so many waste products in and around the muscle cells that they cause the muscle to degrade/not function properly (ie. lactic acid etc.). While it's really doubtful that you would use your flexor and extensor muscles in the hand this much, it would still cause wear and tear of the joints, and accelerate the process of osteoarthritis which is an inevitable fate for all of us 
How solid is your information regarding osteoarthritis?
I have never been diagnosed with osteoarthritis in my hands but my poor old grampa, his fiingers were all disfigured by some kind of horrible arthritis. He was age 80 or 82 at the time. He died a couple of years later after gramma "accidentally" ran over him with the car.
I have not studied osteoarthritis so I donno much about it other than it hurts. 
Seriously,
remind me not to get on your bad side. These things run in the family...
)
and for the "right shift key" swap it with COLON.. and if your left hand shifting hurts as well, swap it with Caplock...
Use "scan code remapper for windows nt" it comes in a utility pack from microsoft, works on window 7
The custom layout below I've made is to get rid of wrist pain, and removes alot of hand movements.
it is also 1 column wider.. which provides better shoulder comfort.
Your idea is very similar to mine!
In my idea I was going to simply scoot everything over kinda like you did but then I would put my SHIFT key where the "H" key currently is.
Then I was going to force myself to relearn the shift key being in the middle.
The advantage of my idea is that then I am
not using my pinky to shift. The pinky key is way overused on qwerty keyboards.
The disadvantage of my idea is that its harder to learn and I can't shift without removing a hand away from home position.
If I use your idea then:
- Still using Pinky to shift.
+ Can type at full speed without removing fingers from home position while typing shifted chars.
I could implement
both ideas! And just move 1 key out to the numeric keypad.
Then I could at least try my shifting in the middle thing every once in a while to see how good or bad it is. Maybe I could gradually work my way into it.
Is there a reason that you said to use "scan code remapper for windows nt" instead of that other proggy that everyone always says to use? (I can't remember the name right now)