Modern game includes no mid-court or net play?
Mick you need to do some research into what top academies and coaches are teaching. The reason why most players have abandoned the net isn't because they don't know how to volley, or cannot handle mid-court balls. It is because its not a high percentage play anymore to come to the net constantly at a high level. A player is too vulnerable up there. Also, instead of coming to the net players finish a lot of points mid-court. Current players are better in the mid-court then 20-30 years ago. They are hitting harder, stronger shots, more angles, etc from there.
Coaches nowadays teach all aspects of the game, its ridiculous how complete a lot of training programs are. All areas of the court are covered, all tactical situations etc. At Sanchez-Casal for example they pay as much attention to net play as they do to mid-court and baseline play. The reason why players choose to play at the baseline is because that is the nature of the game now and their best shot at winning. It isn't the coaches forcing kids to play only from the back.
If there was any loop hole, anything missed it would be covered and used a long time ago. Top players look for any advantage they can get and coaches scout, analyze, and teach the best way they can for their students to win. Also, you cannot force a player who is comfortable and has the mentality to play at the baseline to all of a sudden expect them to become serve and volley'ers, it just doesn't work that way.