[KK7NIL]

The only scopes using frequency mixing are the LeCroy scopes over 33 GHz and these have been commercial failures.

All the other scopes on the market use time interleaving (time multiplexing) which has much better characteristics but requires that the ASICs have much higher Ft, which requires a significant capital investment.

Sampling scopes are not actually that much cheaper now a days, especially after you take into account the cost of the clock recovery device that you would need to build a proper eye with a sampling scope (I discussed this further in other parts of this thread).