I currently run SD on an iPad and on a Nexus 5 phone which I stick on the side window for a "HUD". It isn't easy doing route changes etc. on the phone, so would it be feasible to link the two together in flight so I could make changes on the ipad and it would be reflected immediately on the phone?

You can do this with two iOS devices by taking advantage of their Airdrop technology. Going iOS to Android without the internet isn't doable with SkyDemon though.

Route -> Share is exactly how you share a route via AirDrop to another iOS device.

We do not restrict the apps or items which appear in that menu. That's up to iOS.

We add a whole bunch of file types when the user picks Share, from the native .flightplan file to HTML briefing output to a GPX file and others. I'm not aware of any more we can do to encourage other apps to display themselves when confronted with such a list, but am open to suggestions.

I am the programmer, and I have done so. I do not know the answer. The only thing I can think of is that perhaps the apps you are expecting to appear only deal with single-file Share activities.

I am a new (and very impressed) user and I have a similar suggestion/ request: I fly a tandem aircraft currently with two Skymaps front and back, (plus a skydemon now of course) and when I fly with my other half (who also flys) the person in the back does the Nav and Radio and the driver does as he or she is told (!)  I would eventually like to be able to sync two android devices so that any changes in the route are reflected on both devices. Perhaps some sort of a master and slave arrangement over bluetooth, is this possible?