Ok dude this is somehow heavy stuff, but its expected given the fact this is a thesis.

Google actually has some kind of the swarm-based scent trail system, but it is highly ineffective

It might be difficult to catalog it as ineffective because at least in my case, I don't have anything to compare it and really know if it is effective or not.

From my humble point of view it would be much more effective if the users themselves could spent their time to leave the “digital pheromone” consciously

Yes, but it will be much slower as well than just using algorithms. The rewards for taking the time to leave the pheromone would need to be good so people can justify themselves to spend those few seconds on every site they visit, it might seem like little time just spending a few seconds but I can add up really quickly.

Maybe artificial intelligence is the solution?