As long as the setup limitations is not available in server options I don't think the ABS will give a huge amount of advantage on road cars.
Even now, on the current Z version, mouse or keyboard users tend to lower their brake pressure to avoid locking their wheels and still manage to go as fast as wheel controller users.
But in the long run, when the tire physics are improved(especially when the longitudinal grip varitaions get more realistic) and wet conditions on the tracks be available, this could be a big advantage on hotlaps and races.
As SamH already said, it would be good if we can have at least the server option to restrict ABS.