I came across this again through search. We still haven't made a decision on the self-referencing question in JavaRosa.
However, dynamic defaults have now been added and remove the need for the self-reference in @Xiphware's form when using a value from the last repeat instance as a default in the new instance. You may be interested in an XPath-based solution that I shared at Error dialog when downloading form with last-saved - #4 by LN. It should be possible to write the same with indexed-repeat.