There were already some 'Codeplex smells'... And my own efforts at porting Umbraco v5 over to Linux kept pointing to the extremely complex, perhaps overly complex, Hive.
Yes, the Umbraco Hive concept, an all encompassing aggregating data source that was going to be extremely fast, easy-to-use, and that was to replace the original XML based storage concept, proved in the end impossible to implement.
As the Hive was central to everything in version 5, the failure of the Hive, in my opinion, condemned the application to early extinction.
Umbraco 5 had been in the pipeline for about 2 years. It joins the long list of prominent Edsels, which the computing industry has produced... It is surprising that even in this Agile age, such a big mistake went unchecked, grew, and forced the project to be abandoned.
Sometimes it is difficult to let go - especially when we are passionate about something. In this case, both the Umbraco community and the Umbraco team had placed such high hopes on version 5 that it took quite a while before anybody said, "It is time to stop."
While the passing of version 5, and the circumstances of its passing form a sad note, it is also valuable to notice that the Umbraco team has acknowledged that version 5 was essentially a "dud." And they have done the right thing.
Furthermore, going back to version 4 is not such a bad thing, as version 4 is a very strong product, and will even give us XSLT back.