The community library is ‘forked’ with each release.
So you can commit versions changed for 2.0.0 without fear of breaking 1.0.12.
So I’d not bother with backwards compatibility generally.
With a small and dynamic community like axoloti , I think moving forwards is the best strategy rather than trying to spend undue effort supporting the past. (*)
(*) Of course 1.0.12 continues to work unchanged
, so we are not talking about breaking things - so those on 1.0.12 can stay there until they are happy 2.0.0 is stable enough for their needs.
Those who want to help move axoloti in can progress to 2, and help achieve that stability 
Technically,
objects that are saved with the 2.0.0 editor, are ‘upgraded’ to 2.0.0 and so are not loadable by older versions on axoloti.
So things like using #ifdef won’t help much 
( Axoloti reserves the right to change the xml format , not sure if this happens in 2.0.0 or not, but it does update the object version tag to prevent loading in 1.x)
Note: many objects developed for 1.x will continue to work unchanged in 2.x