I have noticed some BBcode missing, Many functions are differnet now, and later will not be compatible. As also later the functions will be renamed away from sed_ to cot_
So, I think we will have to have some sort of modified legacy functionality. Essentialy wrappers in some cases, and in some case's possibly modified functions to work with things we have now.
I would recommend we have for loading plugins, a way to detect these, and possibly as needed flag them as special. And then load legacy files as needed. The only other possiblity is to for them to make some manual changes. This of course would be the most recommended route.