There's something in what you say, but consider that we have pretty
much unanimous agreement that 10 is too small. I think we should
try to fix the problem, not just gradually ratchet up the value until
people start complaining in the other direction. (Also, we should have
plenty of opportunity during beta to find out if we went too far.)
I am not sure if entity-attribute-value model could be used for postgres database, however that is one of the cases that require large MCV list (generally, for attribute column).
You know, Oracle is not able to store more than 254 distinct values for histogram statistics. That really limits the use of histograms for software product the company I work for creates.
One more direction could be implementing "MCV" for range of values (group values and interpolate in between). Consider statistics on timestamp column that says that for "2008-December" there are as many X rows, for "2008-November" as many as Y, etc. That could be used for rather accurate cardinality estimation of "between" cases, while keeping number of entries in "MCV" list small.
Regards,
Vladimir Sitnikov