When I saw (what I assume to be) the letter r I thought
Kiznaiver but that was already announced thus not really super secret and the disc count and time doesn't match up either.
In terms of Classic shows,
Oniisama e... (
Dear Brother) is getting a BD in Japan but it's a 5 disc release (Discs 1 to 4 contain 8 episodes each, Disc 5: 7 Episodes + Bonus Footage) so I doubt it's that even if I wish it was the case.
Gunbuster is 6 episodes so it wouldn't be that (damn it)...unless it came with
Diebuster which would fit the 4 disc count altogether (I'd die and go to heaven if this was the case)
A
Patlabor Movie collection would be a three disc set unless it came with bonuses such as the
MiniPato OVA on a separate disc. Unlikely.
Mach GoGoGo (
Speed Racer) which Funi are releasing wouldn't fit on four discs.
Outlaw Star is a four disc set so that seems likely, or it could be
Lucky Star or something?
Of course this is all keeping in mind that it might not even be an r. Time will tell. We can say for certain that it is not