> So Indexes with snapshots will be degrading the performance only for deletes > and only those updates, which are updating the index tuple.
Deletes never update indexes in Postgres. Increasing the size of the index would affect vacuum, inserts, and index accesses.
In the new proposal, deletes are going to update indexes. So its a trade-off between selects and deletes, since selects may not need to goto the table for checking visibility. You may go through this thread, to get more details.