Version neutral XPath: Define XForms in a way that is (largely) independent of which version of XPath is used.
Introspection functions: Discovering which parameters event() and property() accept
Sorting: Define our own sorting function, or soemhow use XPath's (which depends on which version of XPath you have).
MIPs on controls: Allowing MIP-like attributes on controls
Data traversal: Traversing instance data depth-wise in a generic manner
Websockets: Declarative packaging of websockets to look like submit
File write/read: Loading and saving files
<control/> and instance mirroring: User-defined controls (with instance mirroring)
collapse="open/closed": Allowing groups to collapse and expand
State change events: Catching things like value-changed within the model (and not just the UI)
Submission echo: Not needing a server to see what you are submitting.
Repeat with automatic controls: Declaratively specifying what the user may do to repeat-items (delete, edit, insert etc).
Tabbed appearance for select/select1: Another representation for select/1 with tabs
Input suggestions for select/select1: Supplying an automatic suggestion mechanism.