I am thinking in quite the opposite way.
Firstly, if we move 40,000 troops to the India-Tibet-Bhutan tri-junction, it will increase border tensions. On the other hand, we cannot keep the troops down in the plains. We must keep the troops in the high altitude regions, infrastructure or not infrastructure, and that will not only keep the soldiers acclimatized, but also give them practice to keep supply lines open when there is no infrastructure. This practice will prove invaluable in case of war.
Moreover, what you are saying is a 'flat region' is quite the opposite. You should look at Google Earth and see it for yourself. Armoured assault in Arunachal Area is a no no. CAS has its difficulties, but is not impossible to master with practice. In case of another war, it will have to be fought with troops that are used to living in the woods for weeks without supply or quick access to infrastructure.
You should see the concept behind training the CRPF Cobra units - they train by doing extreme hard work. They are trained to work as autonomous units, without being detected, and without getting supplies for up to 10-11 days. See the video here:
http://defenceforumindia.com/forum/internal-security/51237-make-naxals-our-own-assets.html (Opening Post)