From what I've heard direct from a Jolla enginner:
1. Sailfish is lean. They had it running on a Raspberry Pi.
2. Porting Sailfish to the N9 will be difficult because of its closed hardware. The N900 is comparatively open and better understood. Only the GPU is closed.

I dare say it will be ported to the sold-at-cost Nexus 7 either way.

And presumably ACL will be closed source.