I spent a few minutes with an ESRI staffer involved with the move to support PostGreSQL (an open source database that’s widely used for spatial via Refractions Research’s PostGIS). Here’s the plan which he stressed is tentative. He noted too that its in early development, so alas was not available to demo at FOSS4G.
PostGres support is expected with ArcGIS 9.3 next year (Q1 or Q2).
Support is planned with Enterprise ArcSDE, which means users will need ArcGIS Server Enterprise Basic at a minumum.
The support will include both the PostGIS spatial type and ESRI’s own implementation of spatial in the database.
All the existing ArcSDE funtionality (versioning, transactions, etc.) will be supported. And, there will be SQL access to the geometry (which is based on OGC Simple Features).
Windows Server 2000/2003, Red Hat Linux ES/AS both 32 and 64 bit, SUSE, Solaris.
ESRI is very interested in feedback and those interested are pointed to the soon-to-exist ESRI product forum for the beta.