This is just a quick progress report after two sessions of practice. I hit against the wall and did shadow swings yesterday, and today I hit with a friend.
I really like the straighter arm for the forehand, at least until the forward swing starts. I am not really trying to do ESR, but I feel like it is happening automatically as I point the racket butt at the ball. Probably the forearm supination and ESR are melding into one motion. Pushing off the ground and starting UB rotation just seems to fling the racket forward - this did not happen before as strongly as it is happening now. The arm seems to be more wound up and connected to the body. I practiced with a higher level player today, and he was all smiles and approval at the change, so it seems I am doing something right...
I decided to break up what I am doing into a small progression. I am not trying to spin the ball as usual or hit too hard, although the basic action seems to have spin and pace built in. Once I feel comfortable, I will do my usual spinning action with the wrist/forearm (pronation, I believe). When I get around to making a video, I hope it will reflect the changes I am feeling, but I am getting used to not looking like a pro on video, lol!
Another thing I am doing is incorporating this concept into my two handed backhand. Just keeping the left hand straight and pointing the racket butt at the ball seems to do it, similar to the forehand. The extra power is nice... makes it easier to hit deep!