Well, there is no use for BlobID of created blob in driver outside Cursor._pack_input, as it's pure transitional information. I also don't see how this information could be useful to any driver user. As it's definitely not easy to pass such data from deep internals up to user level in some sensible way (it must go along with other BLOB identification in context of the SQL command, otherwise you can't distinguish between multiple BLOBs), I'd like know at least ONE good use case beyond internal QA test for one bug before I'll commit myself to implement this feature request. I really don't want to complicate the code and API, and make insert/update with blobs a bit slower for something that nobody will really use.

at least ONE good use case beyond internal QA test

One more ticket has appeared where such feature could be used: #8513
(QA test for it was implemented by parsing of ISQL output)

Well, I was after use case from Firebird application such information would be needed, not more QA tests that want to peek into Firebird internals. If you want this information in tests, then these tests could be written using the OO API directly as the Python driver provides all needed interfaces. You can even access interfaces wrapped in driver objects (Connection, Cursor etc.), see Connection._att for iAttachments or Cursor._stmt._istmt for iStatement.