The needed technology advancements don't have to come as a direct result of investment in an aviation solution. Most of the the best recent advances in general aviation have trickled down to us. GPS, flat-panel displays, tablets, etc were all developed for other applications and only leveraged in aviation after the technology matured. In fact the current diesel technology that they are trying to apply didn't come from advances in aviation research. The breakthroughs that have made diesel even a possibility in general aviation have come from the auto industry. There is no reason to believe that automakers will stop trying to make diesel engines lighter and better. Ultimately we might benefit from that.
The first couple of generations of diesel cars were failures by most criteria. New technology including new materials and digital engine controls changed that. The thing about disruptive technological advances is that few people see them coming.
I get why some are pessimistic about general aviation but I like to look at things like WAAS GPS approaches and in-cockpit weather (XM or ADS-B ) and I am amazed at what this technology has brought to an industry where the "ROI looks pretty poor". Given the choice I will always remain optimistic regarding new technology that we can't even conceive of today.