I can actually think of a few reasons why this might not be such a great idea:
1. It appears to alter the output of every file on the server, this means it has to look at every file and compress it. Whilst this may be a good option on a single site server, on a server with thousands of accounts the CPU load required just to compress every single object would be prohibitive.
2. By compressing every object you are going to seriously confuse an awful lot of people, as they will be receiving code to there browsers that looks different to how they coded it; this make debugging errors in this code more difficult as you have to first interpret what line of code the compressed code is referencing in your code.
I therefore can't see this being much of a valuable addition to the servers, plus you have to factor in the time it would take to configure it properly. I'll repeat what I said before then, if you really feel you need this then you could opt for a VPS server.