Submitting your vote...
TYPO3 5.0 discussion has started in the mailing lists. I could not find any references to architectural documents but there are discussions about specific details already. It does not look right to me. If you have bricks, it does not mean you can build a nice house. You first should have idea what you want to build, you should have sketches, plans, etc. It is not time to care about wallpaper color if you have no idea what exactly you want to build on a general level.
I am in particular feeling bad about selection of JSR-170, Jackrabbit and PHP-Java bridge for data storage. This will be terribly slow.
Let's see how it goes...
As far as I understood Jackrabbit and the PHP-Java mix is only for early development. The PHP-Java bridge is needed to access Jackrabbit as long as we don't have a JSR-170 PHP implementation. It's said that development will start with developing an php interface to Jackrabbit and a JSR-170 PHP implementation at the same time. As soon as the JSR-170 PHP implementation is finished Jackrabbit gets exchanged by it and we're rid of Java.