Hey folks,
Although as somebody with a web fonts background, I am of course familiar with subsetting. But I am wondering if you could flesh out a bit more detail about what you would want from this feature and how it might work:
1) In font editors
2) In TransType
I can say that an obvious first step would be that a font would not fail to compile just because of missing glyphs—even if those glyphs were referenced by OpenType code. But after that, it gets complicated in terms of user interface and options.