I'm sure there are people that are totally happy with the original Axe FX and the 2, and I'm happy with my 3.
At this point, I don't think Fractal will change the interface, which I think is the only weak point of the package, but I don't see me perceiving the tone as getting better - I couldn't tell the difference between real amps and demos when the 3 came out and we're many iterations of software later now. Maybe a smaller unit with the same amount of power would make sense, but given the 3 is fairly empty inside and the size of the unit would appear to be dictated by the screen, I'm not sure that a smaller unit would be perceived as better.
If I was in this business, I'd probably be tempted to release new hardware once the sales start to taper off, but given that there's just one Axe FX 3 on Ebay right now (UK), I assume the demand is still there, so I wouldn't have thought the time was now.