I just watched UK-TUG 2012 - TeX Gyre Math report, and it wasn't clear to me if the characters of existing fonts are being adapted to the OTF formats, or if all-new glyphs are being created. For example, one of the fonts being worked on is Times, via TeX Gyre Termes (Nimbus Roman No9 L). Are the new math characters brand new, or they adapted from some other source, such as mathptmx (URW Nimbus Roman)?
The glyphs being created are new. The 'text' part of the TeX Gyre font project (completed some time ago) focussed on the glyphs derived from URW's fonts, but this only covers 'text mode' requirements. The current work is focussed on math mode glyphs, and these are not 'already available'. As such, the project involves a lot of new work on glyphs (there is other work on how to actually construct Unicode math fonts at all!).
It's worth noting that existing bundles such as
mathptmx are something of a mix of glyphs from different sources, some one which actually fit and some of which are 'better than nothing'. As such, the work being done by TeX Gyre (and other math mode projects) is substantial.