First, there are no fixed lens cameras that come anywhere close to the RX10iv. So, one would have to go up a level.
Well, let's dream a bit. How about a Sony A6600 APS-C camera body? Now there is no single lens that covers the 24 to 600mm zoom range. But we can come close. Trying for a minimum number of lenses, how about a Sony 18-105 which is equivalent to 27-157mm. Then Sigma makes a 60-600mm lens. I have not researched every lens out there, or perused the reviews, but we are dreaming. So, let's see, The body costs $1800. The small lens is $648 and the long lens is $2000. I am up to almost $4500 without any sales taxes. Yike! That would never get by the CFO (wife).
I am sure there are lots of other lens combos, but as I said, I have not delved that deeply into it. I am well over my budget in any case.
As I see it, there is no way I can match what I already have for less than around $3000. I seriously doubt I will be getting enough improved IQ that would be visible without very deep pixel peeping. I owned an A6000 with the kit lenses. I did not see an increase in the IQ between that combo and the RX10.
Don't even think about the extra weight. That long zoom weighs 5.5# without the camera body.
So, even if I hit the lottery, there does not seem to be a camera option out there that can beat the size, weight and zoom range of the RX10iv.
Jerry