> enable a --quiet / --verbose mechanism, so that those who don't
> understand most of the output meaning can omit it.

OK,  I perfer to use java [options] -jar splitter.jar ... > splitter.log, but I  add that to my todo list.
The list looks like this now (no specific order), let me know when you like to add something:

- optimize memory requirements in ProblemListHandling phase
- try to optimize memory requirements in pbf and o5m writer
- use thread(s) to interpret input file
- limit generated problem list to ways and relations with type=multipolygon or type=restriction
- report only those parameters that are in use, or report two lists, one with the user specified parms and one
with those that are in use
- add --verbose parm to suppress anything but errors or warnings in stdout.

Gerd