I'm rather curious about this one. JB maps aren't really made with VSH in mind, meaning they have lots more resources available to the red team. More ammo and health (albeit in a single or few locations), lots of chokes for the engineer to build in and make it near impossible for the hale to reach them, and adding reviving might make those engineers and annoying classes a hell of a lot more annoying to deal with, also extending the round. I'd like to hear other people's arguments on this.
In my honest opinion, vsh already feels really long and I feel adding med will only my them longer. Many people don't enjoy vsh much and play jb for, well, jb. I believe the red team already has a good enough chance against hale and adding med will just extend the rounds and make vsh more annoying.