I'd want them to drop CP alltogether, at least as a gym placement criteria, it makes for a pretty boring metagame, people just put their highest CP pokemon so they are placed higher, regardles of how good or bad they are as defenders.
As a side note, the last adjustment wasn't a CP adjustment, it was a modification of how the individual stats (ATK and DEF only) of each pokemon were extrapolated from the stats of their main series games counterparts, to better mirror said games.