At the ESRI Developer Summit there was news of the File Geodatabase (FGDB) API. Based on the tweets from the summit it appears:
The API will be C++ only
API works on Windows and Unix/Linux (specifically RedHat, Solaris, SuSE) operating systems
Rudimentary support only---features such as annotation, relationships, topologies, etc. are lacking
Since ESRI is releasing a targeted API and a not a specification, support for Mac OS X is out of the question.
How well open source GIS applications will be able to support the FGDB (if at all) remains to be seen.
The other question is: Will the API be made freely available or will it require an ArcGIS license?
Will the release of the FGDB API be the "Shapefile-killer"? I have my doubts...