The Schema in AD is just a set of meta-objects, I believe they have something like an API to extend this list. We need this API support in DSfW as it'll solve a lot of issues with incompatibility of other solutions with DSfW: like Exchange support, for instance, which is really important for many customers (we have an idea registered here in portal).
I have another idea here in portal about PAM-DSfW integration: I believe the only problem with such integration is impossibility to extend the schema, PAM (actually SecureLogin which is bundled with PAM) needs some additional classes to store credentials etc. It can't extend Schema so Application SSO functionality just unavailable. The only way to fix this is to allow PAM/NSL to extend the schema.
As I said, there are much more apps which needs schema extensions so adding this functionality will seriously promote DSfW. Please add it.