Hi,
First of all there is no 1.8 or 2.0 version in a few days there will be a 2.5.x version which right now is in final (or at least close to that) beta version.
As for the 1.5 version it doesn’t support mobile layout and therefore i suggest that you should go with the 1.7.x version that does support mobile layout and tested with 2.5.x beta version of Joomla works fairly good. (tested on localhost not on a live site)
As for the update for J2.5.x version as you already know JA is trying to keep up with the latest version of Joomla always and although i can’t provide you with an eta about any new version for this template it’s most possible that there will be an updated version for Joomla 2.5.x
I hope that my answer addresses your inquires! 🙂