The Hyperscalers are often working with a company like Broadcom (the elephant in the room on this topic) to design said chips. They don't usually have the amount of ASIC and Networking and Optics hardware expertise in house that would be required. See, for instance, Google's TPUs. Broadcom's hardware people are world class and some of the best paid in the business. It's the most elite hardware company in a lot of ways in terms of total comp for top engineers.
Google hires some hardware people to come up with general requirements for specialized stuff like ASICs, then sends those requirements to Broadcom to do the hard parts and negotiates big multi-billion dollar contracts with them. OpenAI did the same and contracted Broadcom after liking what they saw with the TPUs. There are several other Broadcom customers that I'm probably not at liberty to disclose.
But no, as far as GPU replacements are concerned, the Hyperscalers generally are not experienced enough in the specific types of hardware required to do this by themselves. It's very specialized and boutique high price work and more difficult than say, designing an ARM chip (something a company like Amazon or Google could probably handle in house).
In general though, yes, I agree. Hyperscalers are trying to reduce dependence on NVIDIA. Many are quite far along in their ASIC projects (Google especially, they are on their 8th generation TPU! Way past just being a small scale experiment by now.) and have large volumes of them running in place of NVIDIA chips and much more efficiently already.
Broadcom is fabless, and uses TSMC for these sorts of chips. They are mostly a boutique design "mercenary" firm for exactly this sort of specialized hardware for Hyperscaler customers and other clients that run significant amounts of infrastructure in house (so, think JP Morgan for instance). That's the core of their business, along with increasingly Infrastructure Software in the form of virtualization and mainframes and private and hybrid cloud (so some natural sales overlap there, just generally, "big companies that need specialized big data center hardware and software").