Andrew Eddie, Joomla co-founder and core developer stated following on Joomla's people portal:
Finally, the developer portal outlines the new development strategy that is now in process: http://developer.joomla.org/strategy.html
In summary what this means is:
Release Date Maintenance Till Joomla 1.5 Jan 2008 Apr 2012 Joomla 1.6 Jan 2011 Aug 2011 Joomla 1.7 (Bowerbird) Jul 2011 Feb 2012 Joomla 1.8 (Cool Name?) Jan 2012 Long Term Support
Developers who are concerned about the magnitude of change should monitor the JFT closely to ensure there are no surprises that affect them. Given there is less than 3 months left to accept contributions for 1.7 (and these must be in fully working condition), it is likely that 1.7 will be a very "light" upgrade from 1.6.
- Joomla will release a new version of the CMS every 6 months, starting from Jan 2011 (the 1.6 release).
- We are actually in the Joomla 1.7 (Bowerbird) development phase.
- Development contributions for 1.7 are currently being accepted and should be made via the JFT, either by patch or referring to a branch.
- Nobody can say what will be in Joomla 1.7 until the JFT is analysed and contributions are accepted.
- Developers have the option of working on features that may take longer than six months to develop and target a future version (eg, skip contributions for a major feature in 1.7 because there simply isn't enough time and aim for 1.8).
So what is JoomlArt doing now?
JoomlArt is a dedicated solution provider for templates and extensions that work on top of Joomla platform. For us it is important to be compatible with the most used and most current versions released. Always! Due to a very short support frame of only 6 months for J1.6, we are afraid that we will not be able to convert all of our 100+ templates to J 1.6 in time, like we could do for J 1.0 to J 1.5.
We have currently updated our 17 templates and 30+ extensions for j 1.6 within 2 months and hope to convert some more and then move them all to J 1.7. It is believed that J 1.6 to J 1.7 upgrade would be far easy then J 1.5 to J 1.6 and we are counting on that.
In short, we would be supporting J 1.5, J 1.6 and J 1.7 till there maintenance date, however, not all the templates would be available for each version instantly, some older designs may have to wait for their turn.
My sincere recommendation for now would be that: (a) If you or your client need a site that is not dependend on lots of heavy-duty 3rd party extensions (not yet J 1.6 ready) go directly with J1.6. If your extensions are still J 1.5 version and you cant wait, then J 1.5 is still a viable option with official support till Apr 2012.
I recommend you read the much more extensive commentary by Andrew Eddie about "when to upgrade to Joomla 1.6".