I thought I would list a few things here in a post that I’ve discovered since proposing the ETL Markup Language group.
Metadata Integration has a product called Metadata Integration Model Bridge (MIMB - http://www.metaintegration.net/Products/MIMB/), which translates between various vendor standards for ETL & BI components.
Common Warehouse Metamodel (CWM – http://www.omg.org/spec/CWM/) allows interchange of metadata information between tools, platforms, and repositories.
Business Intelligene Markup Language (BIML - http://www.varigence.com/Products/Biml/Capabilities) is a markup language covering ETL, schemas, dimensions, reports – but it is currently only compatible with Microsoft products.
Somewhere in between these and other initiatives, there is room for an open ETL standard, and tools to translate between vendor formats and the open standard.