This would be a 24% decrease in the number of Guards, which seems ok, particularly if they’re not good at being guards anyway. (Counts from the 2015-09-24 21:00:00 microdesc consensus in my local Tor Browser data folder.)
Relays with the Guard+Exit flags have had zero weight as guards for the last month (I didn’t look back farther). Every consensus in September 2015 has had Wgd=0 and Wed=10000. So effectively the network has been treating those relays as exits only.
Best, Aaron