I'm working for some time in a concept on what I've been calling Null CMS, which would be simply a content repository with metadata support and authorization. The interface would simply be a search and an edit screen. The data would be stored in Plain Old Semantic HTML (POSH), tags and categorization would be made with HTML META tags, microformats would also be used to allow structuring other types of data. Media files could be stored with an associated html file describing it.
In order to make it fast, I'd use KinoSearch to index all of that, including inexing known microformats and other patterns that could be defined in code. The other requisite for that is supporting UNIX-style permissions (ugo+rwx) so I could have three sets of indices - 1 for each user, 1 for each group and 1 for others.
In the end, this is going to be presented as a Catalyst Model, that will then be used to implement web sites in an easy and clean way - using a specialized cat front-end for sites is very straight forward, I had experience front-ending wordpress which, besides it's weird data modelling (and "weird" is putting it in a nice way), and it was pretty nice.
This could easily be solved with a XML database, such as Sedna, eXist or even bdbxml, but they require an extra level of control of the operating system that would make this project pointless (If I have this kind of control, I'd use Alfresco which already implements everything I need).
Conceptually, something as simple as storing everything in a tar file would solve it, but then we have concurrent access and it fails.
I was wondering about KiokuDB, but I'd still need a storage for kinosearch indexes, maybe it's possible to create a store class for kinosearch that stores it in a relational database.
In summary, I need a solution that could be used in a regular cheap shared hosting (which probably means only MySQL).
The other alternative is using Amazon services, but that would make me too depedant on them - although it would probably be a minor problem, since it's all encapsulated in a model class...
I'd like to hear ideas on this topic... what do you think?