The make your own idea and light weight designs definately come hand in hand. I made my panniers out of 6oz packcloth as the heavy material and 1.9oz as the light material (partially because they were made out of remnants). I believe they will hold up to just about anything. BUT if I crash, then I can replace the portion of lightweight material real easily myself. You can't market that very well... "if you crash, then replace it yourself". However, if I switch the 1.9 with a 3 oz oxford, I would concider them marketable. So you can market a lighterweight pannier to the market, but you would need to market it towards the right people. I've seen that that kind of person doesn't exist in enough numbers to make much money.
However, I've yet to see many manufacturers try to reduce weight in other areas either. Yet again, the market doesn't seem to care.
So in another parrallel to the backpack scene... the best lightweight panniers right now are home made. If the homemade "market" takes off, then there might be a market for lightweight manufactured products, but it seems not at this moment.
Michael... You bring up a good point of panniers being multipurpose, but the simple solution would to have your lightweight set for touring and a heavy set for grocery getting.
OR I could be completely wrong...
Scott
So Funbun... make you panniers now, when the market become profitable, you will be one step ahead of everyone else. In the mean time, you will have a kick arse pair of panniers you can show off.