tweaked planner costs and added TODO
tweaked planner costs and added TODO

Signed-off-by: Andres Taylor <883768b6dd2c42aea0031b24be8a2da40fef4b64@planetscale.com>

mahak/vitess,mahak/vitess,mahak/vitess,mahak/vitess,mahak/vitess,vitessio/vitess,vitessio/vitess,tinyspeck/vitess,mahak/vitess,vitessio/vitess,vitessio/vitess,tinyspeck/vitess,tinyspeck/vitess,vitessio/vitess,tinyspeck/vitess,vitessio/vitess,vitessio/vitess,tinyspeck/vitess,tinyspeck/vitess,mahak/vitess,mahak/vitess,tinyspeck/vitess,vitessio/vitess