It will be great to add command like that… Some times it is very hard to aggregate the routes… If the router can combine some route rules as one we can get a well optimised routing tables… Now I use http://freshmeat.net/projects/aggregate/
I coudn’t agree more 
If it could be made to work properly at OSPF ABRs (controling what gets injected from one area to another), this would be great.
But, in just about any other case I can think of, it would seem to fundamentaly break VLSM.