Fully Indexed Collection

We are creation a large collection with 2 fields and both are fully indexed.

For example :

db.collection.insert ( { x : "sddsqq" })

db.collection.createIndex ( { x : 1, _id : 1 })

Obviously the index is required for fast random access.  Now the only problem is that the index could end up being larger than the document in terms of storage.  More over 2x the storage is required to store the same 'data' (doc and index entries).

Does Mongo have any plans to make improvement similar to IOT tables in Oracle ?

Thanks

Alex Leong