I thought we had a bug for this, but I can't find it. I think it's best for us to use LevelDB for IndexedDB as our backing store. We should see how much of the code we can grab out of chromium and use wholesale to make this initial transition easier.
As far as I know we have no plans to do this any more due to success in optimizing our sqlite usage. Marking WONTFIX, we can re-open if we change course in the future.
Just for the record, SQLite 4 will support a log-structured merge database. http://www.sqlite.org/src4/doc/trunk/www/design.wiki