IMO I'm accepting of Alex to remain as long as he wishes as he is doing a fine job. The chair has additional duties such as doing quarterly reports, board meeting minute reviews, new pmc member changes / coordination, and such. However the decisions made for the Apache Flex project are voted on by our PMC and commiters. To me unless someone else is itching to give being chair a shot, it seems to me like not changing anything is the easiest.
If the decision is made to vote for a possible new chair, I would agree that you must be in the PMC for consideration and it would be beneficial to only have our full time members on the list. -Mark