F3 is very opinionated when it comes to representing textual messages and only provides support for CommonMark. The downside is that messages found in other formats in various forges need to be converted to this pivot format. It means there is a potential for loosing data because it cannot be represented. It also depends on how durable CommonMark is as a de-facto standard and how well supported it is in various forges.
A different choice was made for representing VCS. It could be converted in the most popular one the moment (git). But realistically git cannot be used as a pivot format: converting back is only partially supported, if at all. I would not trust there is a good way to convert a git repository to SVN.
Luckily textual representation, although non trivial to implement correctly, only has a limited complexity and having F3 provide a pivot format to do that seems durable. And instead of inventing a new one, CommonMark seems to be a good base to do that.
This choice was made some time ago and it is good to question whether it is still valid and if there could be better alternatives.
Thoughts?