With the Culver Express seemingly imminent as a new service, I was considering whether it could make sense to have a 3rd 6th Avenue local service to help supplement Culver Local service considering those stations are heavily utilized. Fleet expansion would likely be necessary for this, so it probably wouldn't be able to happen at all until the R211 order, but a possible service that could be implemented is a new route running between Church Avenue and 96th Street/2nd Avenue.
This would provide the double service of providing East Side riders with more access to Midtown destinations while also boosting service on 2nd Avenue until the is implemented. After the is implemented however, it could prove to be problematic with 3 services running on a 2 track line. CBTC could help alleviate that. Another issue is the problem of having 3 local services on 6th Avenue. Service would ultimately have to be cut back on the line in order to support such a service as well, which could adversely affect Queens riders.
Something to think about though, as the current plan of just splitting headways for Culver Local/Express probably is not going to last.