Tyrone and Pixel have said that they have no interest in porting to iOS because neither feels that Cave Story would work anywhere near as well on a touchscreen-only device.As for other platforms, there's still PSN and XBLA. Though Nicalis stated not long ago that had no immediate plans for either platform.
There's the WiiU, but considering that Tyrone had to cancel La-Mulana WiiWare's release outside of Japan because of virtually non-existent sales, I doubt he will be trying it again on the same DD platform that caused him such a loss for a console that is doing so poorly at the moment.
Nicalis is currently porting Guxt and Ikachan (or ported in the case of Ikachan), so there would be no cave story ports in the near future anyway.Pixel has always made the games he wanted to make and continues to do so, rather than throwing sequels at the same franchise over and over like Capcom does. And hey, I commend him for it.