Here is a proposed list of issues to address in the HBase 0.22 timeframe, approximately October+ of 2010 (Was 10/2009 originally but HBase 0.21 is still to be released as of 04/2010). Please modify as you see fit or fill in detail:
Discretionary access control HBASE-1697
Small query language for filters (Better query predicate push down) HBASE-1002
Cluster status and region topology visualization HBASE-1805
Suggestions and Feature Requests
Better testing support for testing HBase client code. Something like MRUnit for MapReduce.