By Matt Rajkowski
Here's the best I can tell as one of the developers (I'm not the decision maker).
1) There are some differences in moving the data from a 5 to 6 system but I'm not aware of any scripts to do this yet. Since version 5 supported over 10 different databases and version 6+ only supports PostgreSQL we were wanting to know more about which databases are in use since there have been thousands of downloads and Concursive doesn't have any records of the database used.
So far in the queue we have MS SQL installations that want to upgrade so we're exploring moving the data from MS SQL to PostgreSQL, but nothing definitive.
2) Versions 6+ had major improvements to the Marketing module so moving data around is required. There are other data changes but very minor. The biggest improvements are compatibility with Java 6+ and Tomcat 6+, as well as performance improvements by using caching and search indexes.
3) 18.104.22.168 came about because a customer sponsored the changes. We were happy to do this but would rather see installations on 6+, so while 5 is not actively being developed and patched, it has happened before and I can't rule that out.
4) Please chime in with your installation details... specifically which database you are using. I'll see about running a poll to gather more info from others.