Yes, actually, I have been heavily considering a scarf on Gengar. Especially to stop the likes of Starmie, considering he can spin block AND outspeed and OHKO. Also, considering that it seems everyone is using choice scarfs on everything, it is definitely a great idea.
The other consideration is running leftovers for the recently loved sub+pain split gengar for added "stalling" tactics, if I do decide to really go along with a poison stall team.