Arduplane add a new Flight mode

Hi all,

I am starting to add a new a flight mode in Arduplane and I am currently trying to find the proper Documentation and whether it is doable with reasonable amount of effort or not.

I found this wiki page Adding a New Flight Mode to Copter — Dev documentation for copter. How relevant is this for Plane?

Also I ve seen a lot of topics with people struggling with this. Are there any changes made in Plane architecture or still remains a hard task to add a new flight mode?