JFS Storage Change API sandbox features

Hi,

We are planning to start using JFS Storage Change API for grouping related changes and we also would like to use its sandbox feature for storing non-committed resources during (potentially long running) editing sessions.
We believe that we need two features in addition to what is already there for a complete solution for RCAM:
1) The JFS Change resource/descriptor does not seem to be extendable. While it does contain the essential data we would like to be able to modify a Change resource by adding our own custom fields to it and PUT it back on the server. Is there a chance that this scenario will be supported at some point?
2) Our change sets are potentially large ones in terms of number of resources included in them. Because of that it is critical for us to be able to index the modified resources even before they get committed. We think of that as, for example, Indexing service becoming Change-aware and indexing resources revisions within a non-committed Change and allowing search requests scoped by a non-committed Change (and never mixing that index data with the actual storage index data or other non-committed Change index data, of course).

We understand that we can do all of above by implementing our own sandbox for modified non-committed resources in a dedicated Storage Area and introduce our own descriptors and use our own indexing policies there but that approach brings its own issues and we in fact would love to build our solution around JFS Change API instead of introducing a home grown one.

thanks!
Gleb