Speaking as someone who experimented with that, doing so actually did not have the benefits which we thought it would.  Introduction points are not actually used very much - essentially once per fresh connection attempt, and then cached locally - and having (e.g.) 10 introduction points to register didn't assist performance, in fact it made recovery times (after an outage) somewhat worse because there were more IPs to register.

This latter is also part of why I stopped recommending using OnionBalance to big sites like Reddit, Twitter & the BBC; simpler instead to run 2 or 3 instances which farm out access to a proper web-tier, since those 2 or 3 instances do not actually have to do much work; this (plus the practice of descriptor caching) also implements an ersatz "round-robin"-style loadbalancing amongst the HSDir, if you tune the tor instances to republish their descriptors at different times. 

- alec