For entirely unrelated reasons, I have looked at some of the related code in the last few days. While most people are unlikely to miss any crucial functionality since it is not even enabled in the default build, there are two comments of the "this feature not yet implemented" kind in the GETINFO section of the infinality diff which is not in the alternative code path. The alternative simply does not mention anything missing.
I hope some of these knowledge in comments, probably also alsewhere, are copied over before its removal. There are people who want to know what Apple/MS does which FreeType does not (yet), even if those corners are practically unimportant and/or nobody is doing anything about it any time soon.
FWIW, those two "not yet unimplemented" features have been not yet unimplemented for 20 years :-).