I needed something like the selectfield but that could accomodate a huge number of values, I refactored the official DatePicker classes so that I could build on top of their functionality. This field will show a fullscreen sheet when touched containing an Ext.List with grouping and indexbar enabled. It should be easy at this point to add find-as-you-type filtering and I may do it in a future update.
Here is the code in case it would be helpful to anyone, I'd also be curious to hear someone from Sencha's take on how I gutted DatePicker and if they'd consider splitting them in future releases so the pseudofield->sheet model can be easily built-on by developers