Yhc needs libffi support, and it's much better and cleaner to have it completely integrated with the core.
I wouldn't say it "needs" it, it would be possible to manage without it, though it's certainly very nice to have it.
Libffi support has greatly improved over the past few weeks, and it will continue to get better. As it's required at the moment it's getting a lot of work and testing, if it wasn't then it would no doubt become neglegeted and not work on anywhere near as many platforms - a very bad thing IMHO.
There is definitely a certain logic to this and if you're happy to get it working then that's great. I simply saying that I'm not absolutely wedded to using it for the core if that turns out to be a problem. But since you're saying "no problem" I'm happy to leave it as it is :-) Thanks Tom