I would take OMAP5 for P2 because with all current OMAP knowledge, I feel I could make best use of it with limited time I can spend working on system bringup. It would also be best choice for achieving near perfect P1 backward compatibility. That of course ignores all red flags Exophase raised (nothing using OMAP5, no support from TI, etc.), and those can't be ignored.
On paper MediaTek's big.little offering looks good too. The GPU driver situation could be overcome with various android compatibility layers (libhybris) and perhaps some custom glue, but is unclear if it would work out, so would be risky. Other drivers should be ok since they have to open all kernel drivers due to GPL.
I don't like all those quad code SoCs, I see them as waste of resources as you have to design for higher possible maximum power usage/heat dissipation that actually needed. But if ED gets good conditions on such soc, I would have no problem working on it.
In unrealistic dream world, I'd really love Apple A7. New, clean, more efficient arm64 instruction set to play with (with full armv7 support for backward compat), very good performance and power characteristics. It would make P2 really capable device, real shame it will never happen.