I'm not trying to sound condescending but I just want to cover a few things real quick for my own understanding through question form.
What makes Federer's forehand modern other than hitting open stance? Wouldn't his forehand be a compromise between traditional eastern grip forehands combined with less range of motion that we see nowadays? Wouldn't Rafa's buggy whip or Sock's let me destroy my elbow and wrist forehand be considered much more modern?
Also regarding the serve, you justify a lot of your reasoning by saying that the open stance serve is analogous to the open stance forehand which I adamantly believe is not valid reasoning. Using the open stance/semi-western serve limits you to only using slice to your dominant side and negates your ability to either hit a topspin serve or a conventional slice serve. I also believe that if one is hitting with the amount of force and torque that professional players use that their shoulder would not fair too well. Whether or not you choose to hit this style of serve is up to you and I would applaud you if I saw you hit this serve in a match, but to suggest that this is some revolutionary untapped technique is more than a bit of a stretch.
There's some other stuff in my head about planes of motion and efficiency and leverage blah blah but I'm not that great at physics and I'm afraid it might end up just being some junk bro-science.
"Using the open stance/semi-western serve limits you to only using slice to your dominant side and negates your ability to either hit a topspin serve or a conventional slice serve. "
You haven't watched my recent topspin practice video yet. Please let me know if you still believe I cannot do topspin serve this way. I'll do another video for slice serve, the forehand way too. Slice serve is the easiest one using the forehand serve method.
https://tt.tennis-warehouse.com/index.php?threads/open-topspin-serve.622371/
"Wouldn't his forehand be a compromise between traditional eastern grip forehands combined with less range of motion that we see nowadays?"
If you pay attention to my dominant shoulder rotation or displacement length, it far exceed the conventional serve range. This is the same as the modern forehand in comparison to older style forehand. The key is angular momentum generation, not linear momentum generation. The modern serve is inheritable more linear than the forehand serve.
Rafa use a lot of wrist radial deviation in his forehand. Federer mostly keep his wrist at full extension state. I like Federer's form and technique more than anyone else.
On the contrary, forehand serve may save your elbow, shoulder problems. Why? The key technique is the passive arm (passive shoulder to some extent). It is less stressful on the wrist, elbow and shoulder. The quick flexing of wrist and elbow, the fast arm swing can cause all kind of problems for these small joints, small muscles. Try forehand serve and compare so you would know.