If there is only a overview of the proposed design I would find it more useful to post it here than to clobber the bug-tracker with it.
It seems that you have already a concrete improvement for the ecommerce package - that would make sense to put in bug-tracker including a patch if available. From there it can be applied by Bartt who as far as I know is the maintainer of ecommerce.
In the case of your planned bboard enhancements I got the impression that you are seeking for general advice before you start, so I think it's better to post them here for a wider audience.
I think there are still some people using bboard instead of forums for whatever reasons, and would be interested in keeping that package maintained (e.g. having bugfixes going into the main CVS etc.). They might not feel comfortable with radical changes, so maybe you should consider making your own version of bboard, for example bboard-enhanced, and make it available to whoever is interested. Whatever is the best solution can only be judged after you posted all your planned changes here.
Btw., for expiring posts you might be able to use existing CR functionality.
