Mediawiki 1.20 stable is expected to come out this month (Nov.) and we are currently testing the 1.20alpha version. It works ok with all non-SMW extensions used on our site (biowikifarm.net) as well as with SemanticMediaWiki, SemanticResultFormats, and SemanticDrilldown in versions 1.7.1, 1.7.1, 1.2.2 respectively.
However, as soon as SemanticForms in version 2.5.1 (or SemanticInternalObjects in version 0.6.9) are added, both normal pages and Special:Version fail.
For SemanticForms the error is:
Fatal error: Class 'SMWSQLStore2' not found in ....mediawiki20/extensions/SemanticMediaWiki/includes/SMW_GlobalFunctions.php on line 279