Even if flash media is getting cheaper, it's still the issue of distribution/market conformity. A console can't have 2 or more different physical media formats to read games from. It never worked and it's obvious why.
So that leaves manufacturers with the dilemma: Go for Solid State tech, get the benefits of low latency, high access speeds and size/heat, but lose out on legacy support, media support and ultimately being cut off of a whole segment of the media market, or go with optical, and it's inherent problems: Slow read speeds, noise, heat, size, but at the same time offer universal support for (DVD, BR, CD etc etc)
I would love a return of flash memory cards for physical gaming, but I simply don't see it happening unless like you said, as an alternate physical option when DD becomes the de facto standard for game distribution.