I simply LOVE TE2013, been a fan since the first version back in eraly 2000s.
So here are my sugestions regarding SLIDING / STRETCHING:
Sliding and/or stretching shots are a big thing in tennis and should be featured in TE4. But how?
I was playing just now and it came to me. When i feel a ball is unreachable, i just try to run full speed towards it, going for the SAFEST shot, wich is engaged by using none of the shot buttons.
So i feel stretching and sliding for a ball should be something like this..... BUT with a "lightining-fast" press of one of the buttons at the last (or appropriate) moment. This quick press, when running at FULL SPEED towards a ball (front or to the sides), would engage a stretching or sliding animation to give that extra help to hit that ball (or not). So you could try to engage it with the slice button, creating that streched squash-shot, the topspin button, so the ball travels high, or even the acceleration button, so, if you're lucky enough, you get that one-in a million shot nadal hit against wawrinka in the final of the '17 french open.
So the difference between sliding and stretching towards the ball would be how far you are from it when you engage the shot. If you're far, you'll slide; if you're closer, you'll only strecth, or slide less. Sliding effectivness could, of course, change from surface to surface.
What do you guys think?