It also breaks two OSX defaults:

  - spacebar on a highlighted item should select it

  - the select menu should open on mousedown, not mouseup.

Otherwise, it's a very nice piece of work.

Maintaining compatibility with existing keyboard UI should be considered essential for accessibility. And I haven't bothered to check compatibility with ARIA.

True but this also supports dynamically loaded data with infinite scrolling and other things that a normal select can't do. I suppose it's a trade off.

Hey, twitter did it with Bootstrap. Javascript is the assembly of the internet so lets get busy re-inventing and then breaking every wheel known to man.

In Firefox on OS X most of the Select2 inputs don't seem to be in the tab order at all, they get skipped over. If I do have one selected and type "new" I expect to see "new hampshire" (or something else starting with new), but it drops the first character, opens the drop down and I have "ew" in the text field.

Pressing a key 'n' times was a crutch for select boxes without a text filter. This is not needed here and doesn't even make sense.

Except people expect select lists to work like that. This is nicely done, but it breaks a number of established conventions about how select lists work.