[vezzy-fnord]

The README for hbase characterizes it differently:

   hbase is a collection of programs that complements sbase
   and ubase. It's meant to be a temporary project that
   will shrink and die once sbase and ubase gets
   implementations of most of the programs included. hbase
   mostly contains programs taken from the Heirloom project,
   but also has other programs, such as patch taken from
   FreeBSD and mk taken from plan9port.

So it's not a rewrite, but rather a temporary code dump for "miscellaneous utilities". Skimming at the code confirms this.

[saysjonathan]

Correct. When I said 'rewrite', I mean 'update of some'.