I think that this is worth a look from the Drupal devs:
http://www.xstandard.com/page.asp?p=463B7CE3-B082-4984-AD84-4A1737959506
XStandard is a well-known WYSWYG editor with remarkable accessible XHTML + CSS output. This is basically a marketing agreement to let open source CMSes integrate a cross-breed version of XStandard (it's the Lite version plus a number of Pro features). Do not know if it can viable, but, as I said, at least worth a look.
From the website:
How The Open Source CMS Program Works
We are making XStandard Lite with some Pro features available to established vendors of open source CMS who wish to offer XStandard as an optional editor in their applications.
-- snip --
This partnership program with open source CMS is a marketing agreement. We offer open source CMS vendors some features in XStandard that we would normally charge for. In exchange, open source CMS vendors offer a prominent link on their home page to the new, educational site xhtml.com. The site (currently under construction) will promote XHTML, accessibility and Web standards.
If you are a vendor (a member of the core development team or an authorized representative) of an open source CMS and would like to explore this partnership further, please contact us at partners@xhtml.com. Open source CMS users should contact their CMS vendor instead, if they would like to see the CMS vendor take advantage of this partnership opportunity.