concurrency settings

As you might imagine while our content has grown so too has the time to index. Is there anyway the concurrency settings of scrapy could be exposed? or some feature to run sections of an index in parallel be added to a roadmap?
 
e.g settings like this
```
REACTOR_THREADPOOL_MAXSIZE = 128
CONCURRENT_REQUESTS = 256
CONCURRENT_REQUESTS_PER_DOMAIN = 256
CONCURRENT_REQUESTS_PER_IP = 256
```