Supporting multi platform from beginning on makes sense for sure and linux/mac/iphone are great markets for indies, but it is difficult to port an engine which has been direct3d only for approx. 7 years.

As toast pointed out it will mean quite a while no new features as time will be needed for porting the core.

I guess a port for A7 will only happen if there's someone who funds this port so they can hire additional developers just for this task.
Due to amount of possible customers this will most likely happen for one of the consoles. Then again most of the consol developers have different (more expensive) tools.