v2 implements a workaround. If PIG_PARTITION_FILTER is enabled, then each index (actual index, not plain validation) is appended as a top-level field to the schema after the bag, and the name has '_index' appended. Thus, if there is an index on a column called 'name', you can use it with a statement like "filter rows by name_index eq 'foo'".
The caveat to this is that we have to relax the putNext function a bit to ignore these fields, so if you have this enabled and are storing a completely bad schema, it will just silently drop your bad fields as well. However this is a small price to pay for the added functionality.