There are pieces of code supporting bzip2 as optional pack file data compression algorithm, there are still options like comprFormat for the Maven plugin, but this has been broken quite a long time (did not track it back, but probably at least in 5.0).
Pack compression is a promising approach of decreasing the size of the resulting installer.
There are now several more algorithms available, which are supported by the Apache commons-compress library. We should make usage of it and optionally add commons-compress implicitely to the installer classpath when a compression algorithm has been chosen by the user.
The pack compression supported by commons-compress should be enabled globally by a tag in the <info> section for all available packs, not necessary to define it at pack file level.