That is a fair question. How can we make snipers an asset in their core role while still making it fun for all the other classes. Snipers in real life aren't designed to be fair or let their enemies have fun. This is why we occasionally see players calling the sniper rifle UP; they want a realistic one shot one kill weapon. The down side of this, which you hinted at is that making snipers more powerful would also make it much less fun for every other class.
Others have proposed increasing sniper rifle damade but giving their rounds travel time bullet drop and windage affects. I would have no problem with this at all. A one hit kill sniper rifle that was a challenge to hit with would seem to be more fun for snipers anyway. The only downside is that CCP has already said they have no intention of adding more realistic weapons physics to the game, citing something about hardware constraints. I'm not a programmer so I'm not going to take up the challenge of battling with the devs on that one.
Personally I think adding a constant sway that can only be stopped by holding your mercs breath, an action which would use up stamina, along with increased damage and lengthened reload times would increase the snipers utility at long range killing while still allowing for other pkayers to have a good time.
In both of these cases snipers should light up on the radar of players in a certain radius when they fire. Those guns are loud after all. I feel like there should be skills/equipment to help counter this effect to some extent though.
Additionally I feel that the snipers need to have an increased risk. It is all fine to shoot people from far away but that distance itself should be the only barrier to people attacking you (or height should you get onto a building). The artifical redline stopping players from flanking and killing snipers has got to go. I know it is there to protect spawns. I was there when MCC camping was a very real thing (REs tossed from the MCC netted me many a kill in those matches where my team got redlined) so I'm not proposing a removal of the redline. It would simply be better for everyone if there was more of a reason to not stay in it such not recieving WP or kills while in the redline or a timer that forces you to move out or face clone termination.
I do realize that neither of the weapon modification solutions does anything for increasing the snipers usefulness in high level games. I'll have to think more on that one since you don't like the idea of making the sniper have the additional role of ewar deployment specialist.