In any case, before there could be a captive runtime, there would have to be a runtime. Regretably, there is no AIR 3.2 for PlayBook yet. Captive or otherwise.
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It has been discussed in other threads. We will probably not hear anything about 3.2/3.2/Stage3D until after BB10 is released. All resources are focused on NDK/Cascade/WebWorks. Additionally, RIM has mentioned that they will need assistance from Adobe to complete the port (RIM has source code rights to AIR). The more people asking Adobe to help would help this cause. Adobe is probably in a better position to do this (but not required to), so lets put the pressure on Adobe so they know there is a large community of developer wishing to use their tools on the BB platform.