Speed up response time of autocomplete widget

I've spent a little time looking at this and a few things come to mind.

1) There is a 300 millisecond delay before autocomplete is submitted. This could be trimmed down, but would not make much sense to do so since you'd then have autocompletes running the moment you pushed a letter.

2) On the back-end, modules implement their own callbacks for autocompletes, so conceivably there is some room for speed up on some of those, but for the most part they are just a single database lookup, so not much room for improvement there.

3) In theory one could have a separate callback file for autocompletes which bootstraps only to the Database level and then runs a query, but this would mean refactoring the whole way in which autocompletes work and to my knowledge this would be ugly and not a very proper way of handling things.

4) What about a solution to this that provides different visual feedback for users when autocomplete begins. Perhaps the autocomplete dropdown shows immediately with a "loading..." text in it or something to that effect, then it disappears as soon as the user moves on or it populates with suggestions if they pause for the response to come back?

4) +1 and it's not too hard to make.

Did this discussion moved somewhere or what is the conclusion?

I would just make it simple. Make it the same way Google made it for autocomplete of search results.
Also What I find troublesome in drupal 7 is that if you write something then autocomplete appears and you only push tab and not select anything you will be left with something written in that autocomplete field but nothing will be saved. In most cases users will see that something is wrong and for example not full title of referenced node is selected. But in cases where you maybe have only numbers, for example you write number "2" and autocomplete offers you 2,20,21... and you click tab, number 2 will ne left in the field but field will not populated ( at least this is the case with autocomplete on entity references, probably the same for other types of fields)?

As far as I know there hasn't been more talks about this. We "just" need someone to take it upon himself to implement the feature request.

I applied this approach in our intranet (Solr + Drupal 6). It worked very well, almost instantaneous.

But ... I was thinking, this issue is duplicated of #1271622: Seek a better autocomplete replacement for core (jQuery TokenInput / Select2 / Typeahead.js by Twitter)
Isn't it?