Where did you find these rumors? Everything I've read indicated that only DOM applications and Flash+friends applications will be possible on the Playbook.
The rumors come from a BGR[1] post saying that the playbook may or may not use the Dalvik VM, without bothering to look into the rest of the SDK and if it would work with QNX or not.
That would be pretty neat - if they could have an implementation compatible enough to only require cross-compiling, we'd be going somewhere darn cool.
Many APIs have had the promise of multiple implementations (and some have succeeded in at least making them, ie OPENstep's many implementations, and Java) but it seems to have not been widely used.
Except, well, unix. Heh, I suppose it has been done successfully.