My experience with a project like this is unless you do reach fabled 1:1 parity, the new tool is orders of magnitude less useful or even actively harmful.

Saving a minute every cycle sounds very attractive, but when a person spends a morning hacking and then finds out the normal tool chain doesn't accept their work when the optimized one did, they will quickly distrust it in the future. It'll also make them very reluctant to share it with their team.

The only reason my project was successful was we ultimately reached a set of compromises with the team that owned the woefully underspecified tool chain and upstreamed large swaths of changes. I would probably never do something like that again.