considering that anope currently does no logging of channel content whatsoever, this wouldn't be a very easy thing to implement, not even mentioning the huge amount of resources that would be required to accomplish this.
Storing the data in memory is no option so anope would constantly have to read/write to disk. Doing this for even a few dozen very active channels would add a serious amount of overhead and also make services much more vulnerable to flooding.
Though the idea is interesting, personally i don't think this is something services should be doing..