Idk, I'd imagine it could still be fun in a series of twisties.. my immediate mind goes to this mad lad on an R3.. I thoroughly enjoy the nimbleness of the smaller classes, i'll still fire up the 250 every few weeks to just go joyride and fuck off.
I think the main concern I am reading is the price, pretty much the original reason the zx2r didn't do well in the early 90's.
edit; ended up grabbing a beer with the dad and brought it up to him, since he his a small bike enthusiast haha.. and his imagination of it, is it scary with that extra power on such a small bike.. Having had pushed a 250 to about 120-ish myself, although the struggle.. could the i4 alleviate that strain and just making it slightly smoother pushing the top end. I know moving into the apex on a 250 feels amazing since its twitcher, but leaving it feels much better on a 600 and a litre. Other than that, we talked about issues in the US with emissions? the power of a small block can only be so much, which could be adjusted aftermarket? but that might be a big prevention from seeing it state side, also seems like its heavily marketed toward the Southern Asian regions where having a 600 or even litre is just stupid.
Other than that, in typical dad fashion; he talked to me about a Gilera he once owned back in the day. Four stroke, single cylinder.. I believe he said 149cc but that I needed to look it up because it sounds super unique..