I've brought this issue up before and believe me it's on my "I wanna" -list. But the cruel fact is that we can't spare the resources for this matter at the moment. Adding more search options is no little operation. A whole new search funtion would require A LOT of work effort and time, which both we can't spare for it at the moment. I've even made a draft what I'd want to include in the new function, so this matter is in my thoughts and who knows what OFP2 might bring for OFPEC.
If you have a specific mission in mind the sorting options we now have should help you find the mission in a resonable amount of time.