by the looks of that report they are only 10% complete. my guess that date is a projected date of completion and it counts down to that time. most likely it will be extended

No the elgg 1.9 is not due in three month... this is wrong (Due in 2 months (09/14/2012) )

Each milestone lists all of the changes - both planned and finished.

I see, so 1.9 is not going to be released in 2 months, right?

The goal is to release 1.9 in 2 months. What is more likely is a beta release around that date.

Maybe it's too early to tell us about the expected plugin backward compatibility of Elgg 1.9 but I'll ask nonetheless: Elgg 1.8 more or less broke backward compatibility with existing plugins completely... will Elgg 1.9 repeat this or can we expect an easier, smaller upgrade leap this time?

Of course, the compatibility of plugins for Elgg 1.9 will largely depend on the code of each plugin but with Elgg 1.8 the changes were so severe that I still haven't been able to upgrade my productive site to Elgg 1.8 due to missing Elgg 1.8 versions of some plugins - and others might have the same problem. Maybe it was only some bad luck of me to choose quite a number of plugins back then when I started my site that are no longer supported by the original developers for Elgg 1.8 and leaves me with the burden to port them to Elgg 1.8 myself. Some other plugins also still haven't been released for Elgg 1.8 even with the original developers still working on it, for example Tidypics and Event calendar. Even plugins officially upgraded for Elgg 1.8 are not useable in any case due to deprecated functions not all being replaced.

The plugin compatibilty cut of Elgg 1.8 might have demotivated some developers already. Others might have accepted it once but might not want to invest the same amount of time and effort to rework their plugins a second time. This might reduce the attraction of Elgg considerably. After all, Elgg core is surely a nice framework but only the plugins make it the basis of a flexible and feature-rich social network community application.

The upgrade to 1.8 was big. It took us a long time to get the community site upgraded. Much of this was because Elgg 1.8 introduced a new framework for HTML/CSS. Rewriting the UI code is time consuming.

Elgg 1.9 will have two big features - a better notification system and comments will be upgraded to entities (to support liking, threading, etc.). Plugins written for Elgg 1.8 *should* just work on Elgg 1.9.

A lot of plugin development has moved to github. I'm pretty sure Kevin has a 1.8 version of the event calendar on there and Brett has an updated Tidypics on there that I haven't taken a look at yet.

One more point - Elgg 1.8 did not break API compatibility at all. It broke UI compatibility. There was nothing we could do about that. Elgg had poor UI code from 1.0 through 1.7. There had to be a compatibility break.

Thanks for the info. That sounds rather promising!

I guess strictly speaking you could say that Elgg 1.8 didn't break API compatibility as such when Elgg 1.7 already deprecated some functions (though the plugins I use originally developed for Elgg 1.6 or even 1.5 still worked with only some very minor issues on Elgg 1.7). When porting plugins to Elgg 1.8 I made the experience that changing the UI part of the plugin costs some effort for sure, but finding and correcting deprecated data handling functions (API compatibility? ;)) was not much easier either as some of the new functions seemed to me to react (or not react) in some rather unexpected ways. Though this might be mainly because I might simply not fully understand the documentation sometimes...

We're still working on the best way to notify plugin authors that they are using deprecated functions. The deprecated functions still work, but they will be removed at some point. We've found that if we don't make the warnings annoying, plugin authors don't update their plugins. We've also thought about scanning plugins that are uploaded to the site and posting the number of issues on the plugin page as a measure of quality.