All true crg, my friend. BUT, if several thousand dollars (or more as i suspect) is required in order to integrate DI into a MB engine (again, unless somebody makes an affordable off the shelf solution) then the topic really is moot. The majority of us will go away or just ride illegally. Nobody's going to retrofit at that cost... they'll just buy a commercial scooter that DOES meet emission standards.
In order for someone to make an affordable system for MB's there has to be 'economy of scale'. They can't do it (and stay in business) just to meet the needs of the few MB'ers here in the states. NOW, if China were to require such for their own populace, the numbers are there and we might see something that would do the job at a reasonable cost. Don't hold your breath.
I expect 2-strokes will just be outlawed eventually, and we will have to transition to EPA approved 4-strokes. I don't like it, but as you imply, there may not be an alternative that IS affordable.
We, as MB'ers, are 'tinkerers'... doing this more as a hobby (or insanity as you state) than as a necessity (of course there are some to whom this is a necessity). As such, we have been finding ways to make things 'legal', but just barely. As the laws get tighter, we'll have to adapt. I don't think we have enough of a voting base among us to enact legislative change, but that doesn't mean we shouldn't try. We'll continue to find ways that allow us to ride and, hopefully, won't cost us an arm and a leg for the privelege.
Good luck and good riding!