James,
Thanks for making a proposal and opening discussion publicly with a solution proposal. As I stated in my private message response to your initial query a week ago:
“If you want my sincere reply: While I understand that this is an easy change with 2-3 simple replace-all statements, I think that this problem should be solved differently than with 2 instances of CB...”
I believe that there are many methods to address your needs with existing CB features and extensions – plugins.
Creating a "second instance" clone (please avoid the proposed term "Community Builder 2", as we are already working on CB 2.0, and would like to avoid confusion

) – hacked CB would only add to the confusion currently plaguing our community

: Joomla 1.0.X, Joomla 1.5.X, 1.5 Legacy plugin, Mambo, AEC hacks, JACL hacks, etc.
I see many technical issues that have not been addressed. Some quick ones come to mind:
- Would you need 2 login modules or most likely a modified one?
- How would user synchronization work with joomla table? (I can just see someone clicking the CB sync tool and messing things up – or will you also replicate the Joomla user tables?)
- I would hate to start addressing support issues and see this bringing up many of them.
- Plugins that have databases (profilebook and cb gallery among many others) will have problems and would also need to be hacked.
- What happens with language plugins?
- You will end up with 2 separate communities, e.g. no PMS/connections/forum between them ?
These are just a few quick thoughts – I am sure there are a lot more.
The CB Team has always been very thoughtful and cautious regarding quick hacks. The team feels that hacks lead to confusion and frustration and of course a hack has no long-term future. That is why the team spent significant time and effort to design and release the CB API. This way real solutions can be created. Solutions that will survive the next release.
We are currently spending a ton of effort to solve the existing confusion above and to make CB 1.2 cross CMS native (Joomla 1.0, 1.5, Mambo 4.5.0 - 4.5.5 + 4.6.x compatible), in a single universally installable package, with a single coherent API

. We are trying very hard NOT to create different versions of CB – one for Joomla 1.0.X, one for Joomla 1.5.x, one for Mambo, etc. This would be catastrophic for our scarce free time. We are also addressing in CB 1.2 many of the current problems of CB users, and designing a solid basis for future improvements. The CB API itself has undergone quite some changes, while lots of efforts have been put in assuring the compatibility of the 100+ existing CB extensions.
FInally, coming back to the problem you are trying to solve with this solution proposal: have 2 different groups of users with 2 different registrations, we believe that with some carefully selected existing plugins and components, and probably an additional plugin and mambot to develop, you can solve that problem more elegantly without any hack in CB 1.1, and without the hassle of keeping the clone up-to-date with future releases.
Some which come to mind are GroupJive, Conditional fields, JACL, among half a dozen others.
CB 1.2 will bring a few more features which will help again, and we are also in contact with the GroupJive team and many other teams to bring those functions in a powerful and non-hacked way into CB.
Hope you now better understand my short answer of a week back