[tor-relays] "Fast" flag definition

Hi, It looks like 94.7% of all Running relays have the "Fast" flag now. If that percentage becomes 100%, the flag will become meaningless. What were the reasons behind the current definition of "Fast", and are those still valid? If not, should "Fast" become self-adjusting ("faster than 2 Mbps or 70% of all Guard relays, whichever is greater")? Thanks!