I think basic iCloud syncing between Macs should already work, just as part of the fact that Bike saves your outlines to some Mac OS file (not database). I know I need to do iOS support, as long as I stay financially viable I will do iOS support. But I still need to work on a few more basics in the macOS app first.

Bike will also read/write .opml files. You should be able to share with iOS outliner that way I think.