I misunderstood your point. I probably switched off (I know I shouldn't have!) after your first comment about DRM cracking - I consider DRM cracking to be a separate issue to DRM aims, but you don't and that's fair enough.
By "hybrid Bluray" I can see now that you're talking about blurays with a writeable area:
(
http://forum.beyond3d.com/showpost.php?p=1628569&postcount=1402)
I was thinking that the cart might need to run a simple check on the console to test for integrity of the console, but if that wasn't needed and you could do it with pure writeable data (which would be preferable as it would be cheaper) then yeah perhaps you could do it on writeable Bluray disk.
Looking at Wikipedia, the IH-BD (Intra-Hybrid Blu-ray) seems to be the closest thing I can find to what you're describing. It's a 25GB read only layer and a 25GB write-once layer. The only blurb I can find on these drives says they'll require "newly-designed hardware", but I can't find out how much the drives and the media cost. Would also limit you to 25GB of data.
I can't find anything from the last year on IH-BD, despite the announcement being in 2010. What are the costs?