I tested a bit the ITST Mod v1.07 (Side note : I won't have the possibility to try out the Online Tour, as my connection is often very laggy in the evening.

I also read a good bunch of match reviews & 1st user experience topics, and both often outline a big dominance of serve, with a lot of aces, due to the return being very hard.
I wasn't sure what to think about that till I tested the Mod, especially as the return is also quite hard for newcomers in the official game.
So in ITST Mod, without any bounce location preview, it is actually very hard to see where the serve is going _and_ to position yourself correctly.
There's a simple explanation for that : either you focus on the ball or on your player => you can't look both at same time (except if your focusing field of view is much higher than mine

I've read complaints about the preview being unrealistic, but as a matter of fact, the current setup isn't realistic as well : in real life, I don't see myself from 10 meters up & behind ; my point of view is bind to my body, so I don't have to look at myself to know where I stand.
Thus the need for the preview presents by default in the official game ; the preview being much closer of our player, it's possible to see it easily while still focusing on our placement.
Thus said, I agree the Danger Zone is an overkill and isn't required to make the game playable.
To confirm my theory of point of view, I tried to play the game with the 3rd person camera : in that case, the camera left/right position is tied to our player, efficiently simulating a realistic point of view. After a few games of adaptation, the CPU almost didn't ace me anymore and it was much much easier to return than with the standard camera.
There's an important issue with the 3rd person view though : it can be hard to feel the depth and I had problem to position myself at a correct distance from the baseline. I did only 1 sets (of 10 games), so I guess with more training it might get better.
There's another issue : you need the 3D courts to use it ; you can't have it with the 2D courts.
And the last issue is you need to have a decent GPU to get a smooth enough rendering.
This positioning focus vs ball focus issue is somewhat same during the rallies, but as the ball speed is much lower than during the serve (especially with the power lowering that occurred lately in the ITST roster), it's way less problematic, and I didn't feel the absence of bounce preview was a fun killer.
So to resume, my point is that it'd likely give a better experience to allow players to use the Serve Preview, if they wish to.