It's not a rumor. It's speculation. That's why nothing else came up with a Google search.Really...?
I literally included a link to my search in the post you are quoting, wherein the first hit was:
Gurman: M2 Pro Mac Mini and no further Studios ?
The rumor of a "one and done" Mac Studio were from a Gurman report
About the Mac Studio, Gurman suggests the first-gen 2022 model will be the only version of the premium Mac ever produced. He explains, "The bigger question for me is if the Mac Studio will ever get updated. It gives the impression—and this is just a gut feeling—of being a short-lived Mac because of its price and niche market. I don't see the purpose of having both a Mac Studio and Mac Pro."
I believe Gurman is wrong here. In order to make a Mac Pro, you must make an Ultra SoC since the Mac Pro will use both the Ultra and 2x Ultra SoCs based on all available reports. If you make an Ultra, you might as well update the Mac Studio. It's not hard to replace just the SoC. Updating the Mac Pro but not updating the Studio makes zero sense.