The latest dev blog post shows some great progress/ideas - as much as I've enjoyed TE3, it's been almost 10 years so it will be nice to play something new and different, and this new animation system could really change how the game feels to play, looking forward to seeing how it progresses!
Regarding the shot speeds/charging, while I understand the reasons you have outlined, I feel a major limiting factor in TE is the way the top spin attribute works and the lack of control over the trajectory of the ball.
Assuming the current TE controls are maintained, on normal depth topspin strokes you only have b1, accel and top spin buttons and each has it's own speed/trajectory depending on player attributes, so you only really have 3 choices. A high top spin stat reduces the top speed of the player's strokes and makes all of them more loopy. Even on acceleration shots from a relatively high/slow ball cross court over the low part of the net, a high top spin character will still hit the shot with heavier top spin and less power than they could. Acceleration shot is the hardest/flattest available but because a player has an average high RPM topspin stroke and therefore high topspin rating in TE, they are unable to play very fast/flat shots when the situation calls for one.
Many players in real life with great forehands, for example Gonzalez, have such an impressive FH because it's so versatile, they can adapt the spin and trajectory to inject the most pace depending on the shot selection. Depending on how aggressive they are trying to play, or the height of the net on that particular shot etc. they can choose to put more pace on the ball at the expense of top spin. I think being able to choose if/when you want to hit flat in TE would really improve the variety and depth of the gameplay, and individuality of the characters if this type of versatility of spin/trajectory was reflected in player attributes. Monfils is another example of a player who hugely varies his spin on the forehand - as he's typically a more defensive player, you would probably give him fairly high topspin in TE, but he's capable of some of the most incredible crushed flat shots and in TE you can't let him have both.
On a related point from your most recent post - while I understand the reason for using the most "common" shots rather that "once in a lifetime" to base the gameplay around, it can leave the gameplay feeling quite formulaic and predictable if you go too far in that direction and leave no space for "highlight reel" moments. I've played TE3 for so long, and while it's a really challenging/competitive game (especially online), I would see no value in a kind of "TE3 best shots" compilation. You can't attempt anything out of the ordinary so nothing unexpected/impressive really happens, in just a few games you already see many shots at the maximum power and all possible ways to win the points.
If you had more control over shot spin/speed, you could try to attempt some different/unlikely shots, and see many more different types of rallies and winning shots. You would need to be careful to not turn it into that TS1 "risk shot fight" nonsense by allowing harder/flatter shots, but with careful tuning and basing the success/probability on positioning and shot difficulty/net height etc I think it could work. However, it may also need a significant change away from the 3 choices of b1, accel and topspin strokes towards either more buttons, double tapping or analog gamepad controls.
Another thing related to this would be that in TE3, net height didn't really seem like much of an obstacle. Playing an accel shot down the line was just as easy and likely to be successful as cross-court as long as positioning/charge was sufficient, have the physics changes in TE4 made the net more of an obstacle at the highest points? How about simulating the difficulty of changing the direction of the ball to hit down the line as opposed to cross-court? This cc vs. dtl shot selection in TE3 didn't really seem to be influenced by the factors it would in real life.
Final point (sorry for the long post and if it's off-topic for the miniblog discussion) - I can understand to an extent your logic around the "charging" simulating the player planting their feet to generate power, but this "charging" mechanic also applies to aiming in TE3, has this changed? For example, if you are on the run and arrive to the ball with only a short time available to charge your shot, you can hardly move your aim away from the middle of the court (this is one of the only reasons volleying is viable sometimes, when you see the opponent won't be able to charge their aim). While I understand that the defending/running player should have more difficulty aiming their shot, I don't think this should be in the "intention" phase of the controls (where your aiming reticle is placed), but in the error calculation based on positioning and the incoming ball. If you are on the run, it should still be possible to instruct your player to attempt to aim the ball near to the lines. Again, this may need a restructure of the control scheme from TE3.