Saw people having the kick starter idea. I saw in the video description on YouTube saying they are also working on a grand piano controller. If we push him hard enough, and there are enough people becoming interested in the prototype, there might be a market.
Who is "him"? CG or this piano technician? There is a market already, but it's small, especially if you are a small fish. Both Yamaha & Kawai have "MIDI controllers" with legit upright and grand action. Ok, they are fully fledged digital pianos, but they can be used as "MIDI controller" if desired. Plus, I think the price of the sound module and the speakers is negligible compared to action and sensors, so it make sense for them to sell the full product to "kill two birds with one stone", so to speak. If you want to compete in the market of new, finished instruments, that's the competition you need to beat.
Also, many technicians can install a key sensor like QRS (or the equivalent PianoDisk) in pretty much any piano. What is special about this guy is only that he's selling it on ebay on a new action-only assembly, rather than retrofitting it in a full, probably old, piano (even though he says that he does that too)
With that said, consider that a good, newly build, well regulated grand action (just the stack, without the keys and the back action) goes for $5,000 so that's the starting point. The back action (dampers) is not very expensive, but their regulation is (at least $1,000 for a well done job). Yet for a MIDI controllers some corners can be cut. For example, the dampers are supposed to lift from the strings all exactly at the same time, with a very precise, long and tedious procedure to regulate. Unnecessary in a MIDI controller, since there are no strings to damp, provided the setting can be done digitally in the key sensor. Other example: in a well regulated grand action each hammer is supposed to strike its 3 strings (or two when the "una corda" pedal is pressed) and none of the nearby one. Seems obvious and "normal", but it's not. That is a relatively time consuming (hence also expensive) thing to do, which is irrelevant in a stringless MIDI controller, so the tricky left-to-right adjustment of the hammers can be very sloppy (ie it's good as long as any nearby hammers do not touch each other...)
Even with that saving, put in a cabinet, shipping, warranty, a dealer profit and the final price won't be much cheaper than N1x or the NV-10 (which have the sound module and speakers too).
Hence, this can be done only by a big company, not a random technician. I think WNG or Steingraeber are two that could. Alternatively, in my kickstarter thread, I suggested CG to target a product for the DIY-from-parts market (including local technicians) who could find a grand action and cabinet basically for free (besides the labor to adjust the action, and refinish or resize the cabinet if desired). CG seems more interested to target DIY-from-scratch people, and given the response we have had on that kickstarter thread (i.e. just one interested party) I think he's right.