Plus, they've already announced the purchase bonus for buying all of the P4 DVD/BDs, and they said you get it from buying the 13 Volumes (39 episodes) they've announced thus far.
I don't believe they'd have done that if they knew they were gonna solicit a few more DVDs and BDs down the line.
They've had two purchase bonuses for Part 3. Buying the 1st half of the season gives you a statue of Jotaro while the 2nd half gives you DIO
EDIT: Picture of both