Im glad you are finding the AutocompleteForMendix widget usfull. It defiently impoves the UX of any mendix app.
As it's been developed and maintained by AuraQ, my recommendation would be to add a feature request to our github and we can see if something like this is possible to add to the current widget https://github.com/AuraQ/AutoCompleteForMendix
However, have you tried adding a second list view on the page (which can be rendered into badges to give you the same style as the sprintr selection). And when the user selects from the AutoComplete widget you can add their selection to this list, and then clear the AutoComplete widget. This will give the impression that they are building up from a multiselect list.