Transmitting NTSC over digital link
Yes it is possible 100%. A little inefficient due to blanking intervals but 100% possible.
You should get some 50-100Mhz+ 8-12bit ADC + DAC on other side.

But transmitting 8x100Mhz signal might be a problem for long distance.

If you are really cool you may encapsulate it into 1G Ethernet :-D