APIcover is used regularly by JCK team fo quick coverage estimation.
It was developed and tested for jdk 1.4.
It somehow works with JDK5 and JDK6 but it's not clear whether data it produces
are correct or anything missed from JDK5/JDK6 point of view (generics are not
taken into account, handling synthesized methods, etc).
APIcover should be tested and updated to support language changes in JDK5 and JDK6.
JCK 6 uses SigTest 1.4 to generate signature files.
But it's impossible to use these signature files with the existing version of APICover since it doesn't support SigTest 1.3/1.4 file format.
APICover should be able to support signature file format generated by Sigtest 1.3/1.4
If SigTest 1.5 will generate signature files in a new format, the ApiCover tool should be updated accordingly to be able to support the latest signature file format.
The existing version of APICover provides final reports only.
These reports are not very convinient for future post-processing.
It would be nice to have not only finally generated reports but row data as well.

Another possibility to make APICover reports more convinient for processing is to provide them in the same format as JCov tool does. It will allow users of coverage tools to process them in a common way.