Negative, the doctors job is already pointless if Chems is working and the fridge is stocked, or the sleepers are upgraded, or the cryotubes work. Anyone that can enter medbay or is let into medbay heals themself anyway.
The point of a doctor is that they need to specialize in fixing oddball problems (infections/genetic disorders) and surgery. A mounted medi-beam that heals basic damages wont change a doctors purpose. Its just a better-medbot. A medbeam wont bring back the dead, it wont cleanse toxins from your body (nerfed version), it wont de-blind you or heal organs or bones... it just performs what synthflesh/pentetic/saline already do.
Ideally it'd be tuned to require uranium to produce as well, limiting it to only 3-4 are produced and attached to bots or healing turrets or given to paramedics.
This is a fantastic idea really. Lets the doctors focus on getting better at surgery (now with the infection PR, surgery is even more labor intensive and annoying which has only made shadowlings and tspiders stronger than ever..)
If youre worried about sec powergaming it, make it take up both hand slots or function as a backpack sprayer, and have a range of 1 tile unless its turret-mounted.