This already kind of happens at Wimbledon. Players are reranked by doubling any current grass court points in their ranking, then adding 75% of their best grass court result from the previous 12 months. It gives a decent advantage to good grasscourt players.
Excluding all non-surface results would be a bit silly though. Do you really want Federer unseeded at the FO because he hasn't played on the surface for 3 years?