I have done some further research and found that the range finder is not something that comes with a special scope or gun, but rather an unlockable gadget that can be added to your weapon like a laser pointer. So you can unlock the Range finder, add it to your gun and then it will work with what ever scope you have equipped. I have been asking for that on the suggestions page of the BF forums for years now, So happy to get it finally.
As for the M82 .50, Yes, you are correct, it is only a power pickup. But I hope it will not be too difficult to pick up if you are quick and careful.
They said there is only one on each map, but... I noticed when I was in a room by my self and playing with it that it DID respawn a new one after a few minutes while I still had one in my hand. So there is only One place to pick one up, but there may be several people able to use them at the same time in a game, so you do not have to wait for the guy to die.
I think you do drop it when you die so some one else can pick it up if they kill you or you kill the guy with the .50
The ammo is limited to 21 or 22 rounds total, not sure if you can reload with a team mates ammo pack, I am hoping you can.
I can not remember if it allowed me to respawn with it if I died, I am thinking it did not.
But we still have access to the range finder on any of our snipers. I think the range finder is a more powerful tool than the .50 anyway. Though the .50 is not an inventory weapon, we still have plenty of high power sniper rifles to play with, Add in Hard Core mode and you are good to go.
But I would not put it past EA some time in the future, to get more $$$$ to add the .50 as an inventory weapon with a special "Pay For" expansion pack of some sort.