Some things I haven't seen discussed but I think are relevant:
1. What is the expected outcome of altering the gas system?
2. In the location of the new gas port, is the barrel O.D. and surface finish compatible with the gas block? Does the gas block have the front sight integrated, and will the new location be compatible with the hand guards?
3. I haven't personally worked on the M&P 15 -- is the gas block bolted or pinned? In my opinion, if you intend to use a pinned gas block, notching the barrel for the pins will be the more difficult part of the job.
Personally, I think the carbine gas system is fine for a service (non target) rifle. It offers more reliable cycling with various ammunitions because the pressure curves of some ammunitions (largely depending on bullet weight and powder speed) drops off very quickly as the bullet goes down the bore. In these cases, the mid- and rifle-length gas systems have a higher chance of gas pressure insufficient to cycle the action.
Also in my (worthless?) opinion, I think problems with over-gassing the AR are overstated. It is not great engineering to have an over-gassed rifle, but the AR gas and BCG components are robustly built and the design minimizes loading.
But, if the thought of over-gassing really bothers you, and is the reason for your project, have you instead considered an adjustable gas block? JP makes one. I have set them up before and they work... and admittedly... do soften the recoil and make the gun feel smoother.
The drawback is that it's another moving part on the gun to wear and maintain. And the adjustment isn't detented, so transitions to and from suppressed aren't very fast if you intend to keep the gas pressure precisely tuned at all times.