The flexibility is worth more than the speed for most flights, and not many of the world's ~2000 billionaires are going to put down a large percentage of their net worth for a fast-depreciating personal transportation device that only becomes worthwhile if they need to leave their continent.

There is another company working on a slightly supersonic private jet (Mach 1.4).

https://www.aerionsupersonic.com

So there may end up being other options.

There's always fractional aircraft ownership. I see ads for it all the time, but I don't know if it's a viable business model.

Fractional ownership works for the likes of Netjets buying existing aircraft types, but it's another niche-sized market and essentially a way for the superrich to avoid buying aircraft.