Thanks for all the questions...
Rough guestimate would be 2-3 weeks (hopefully sooner, but a lot depends on the amount of custom modification projects we receive in the meantime - which is our core focus). As for updates, all of our other themes & plugins for Appthemes to date have run on a free lifetime upgrade policy: Advantage will be the same in this regard. Bare in mind that as soon as Vantage gets updated, we work as fast as possible (resources depending) on upgrading our theme(s) for compatibility purposes. To that end, we mostly stick to front end modifications as this ensures a more future-proof theme.
The idea behind Advantage is to bring it in line with our Prima Child theme for JobRoller - at some stage in the future, we'd also like to do a Classipress child theme with the same look & feel as Prima and Advantage. This way, the user could have a network of websites with a consistent branding across all their Appthemes installations instead of things looking rather haphazard and uncoordinated.
Let me know if there's anything else I can help with