Should this be in scope for Carthage ?

I think that's a good idea, it will be a significant optimalization, fixing many issues with long query node indexing / processing times.

From the mappings, when you get the event context, it returns all the info related to the event/extrinsic, since now extrinsics args info is not being stored indexer DB, shouldn't the extrinsics args property also be removed from EventContext since the args are no longer available.

When events are queried from indexer by the processor, this query is used:

  substrateEventsAfter(where: { ${eventsFilter}${extrinsicsFilter} blockNumber_gt: ${block_gt}, blockNumber_lte: ${block_lte} }, ${idFilter} limit: ${limit}) {
    id
    name 
    method 
    params {
      name
      type
      value
    }
    indexInBlock 
    blockNumber
    blockTimestamp
    extrinsic {
      method
      section
      versionInfo
      signer
      args
      signature
      hash
      tip
    }
  }

So instead of coming from event.extrinsicArgs, the extrinsic arguments come from event.extrinsic.args.
The event.extrinsicArgs was just a redundant, unused field.

So instead of coming from event.extrinsicArgs, the extrinsic arguments come from event.extrinsic.args. The event.extrinsicArgs was just a redundant, unused field.

Ah ok then, LGTM