It would be great if there is a cell (and column) type that lets you choose from a defined list (manually defined list or based on a cell-range). It should be possible to make multple selections and the output should be put into the cell separated with semi-colons.

It should be possible to define cell types (or types that are valid for the entire column) like:
- Booleans (which will result in showing check boxes inside the cells)

The Spreadsheet widget is a good start, here are some additional ideas:

1) Ability to assign specific data columns to a spreadsheet column in DataSource data binding and format them.
	2) Control tools that can be visible in the toolbar as well as add custom toolbar items/tabs
	3) Enabled/Disable or Show/Hide tabs in tool bar. Alternatively, be able to add custom tabs and toolbar items as well.
	4) Events! need more events. Cell selected, Range selected, column selected, etc...
	5) Disable/Enable certain commands (such as Cut, Copy, Paste, Delete) based on #4 or other criteria. Useful if I do not want specific cell or column data copied or deleted.

I want to be able to double click a column header  to set column width to max width of entries - autoresize

Hide or disable Icons, Panes / Functions in the Toolbar

like this: http://docs.handsontable.com/0.18.0/demo-grouping-and-ungrouping.html

Somtimes you just want to give the User a little Side Calc without a full blown Sheet, just the grid with some cells able to change.

Set Fixed Cols/Rows etc. or setOptions( {filter: { ref: "A3:G49", columns:[]}});

Set default Cell Types like Date(Time)Picker, Checkbox, 
SimpleCombo, Autocomplete or own Custom Editor (see other Feedback suggestion)

Define by Settings or via API Calls custom context Menu for any Cell,
like change current by Event BeforeContextMenu(ref ContextMenuElement)