I think from a performance perspective (the kind of thing that would parade around on a spec sheet) the niche would be high efficiency (if you could hit 96db and still get 50Hz out of a monitor-sized box) and a flat 8-ohm load (easy to drive with just about anything). I guess at a glance I really just worry about trying to make something like that, that really stands out at that price point considering all the other options on the market.
It reminds me of the dilemma of the niche companies in the high-end medieval weapons (think swords) market/manufacturing. "Common sense" says that a dagger should cost less than a short-sword, which should cost less than a longsword. Problem is that the materials cost in all the above is negligibly different; the labor costs and production costs are basically the same. This means that for a company that sells longswords at $1000 each, although they can easily make a great dagger, no one would want to pay the $1000 they need to charge for one to make it financially worth making them (unless the profit line is irrelevant and it really gets done as a labor-of-love project). In your case, a few extra board feet of lumber probably isn't much money in the big picture, but it will take just as much time, attention, and care to make a Daedalus-quality cabinet for a small monitor as it does to make say a Muse.
Unless, of course, again you think that your 6" driver could meet or beat your current 4.5". If that is the case - and that 6" driver would then be trickled up the whole line - considering the prices many high-end audiophiles are willing to pay for even sometimes tiny improvements in performance (and the exponential premium thus you are able to charge for that improvement), it could be worth developing the driver mainly as a way to raise the top end of your product line's performance bar up a notch and end up sort of "trickling down" a 2-way that could become a gateway in to Daedalus, although again at the proposed price point, you aren't that far off of a Muse, and a 6" 2-way on a stand takes up a negligibly different amount of floor space as a cabinet for a 8" floorstander...