But in the late 80s and early 90s they actually had the i860 and its variants: https://en.wikipedia.org/wiki/Intel_i860
which contained a graphics processor! That wasn't a particular success but it landed us the MMX ISA on x86.
Surprisingly enough, Intel went then to make similar mistakes with Itanium, and then with Larabee. But both things landed us features on x86.
Maybe Intel ~1998 could have solo-launched a new architecture, but the only way they'd get uptake now is something in cooperation with AMD.
And maybe the AMD partnership bridge is burnt from previous shenanigans, but it seems like both AMD and Intel would have incentive in more tightly coupling graphics compatibility to CPU ISA, vs Nvidia designing their own.
That said, in that hypothetical reality, Nvidia wouldn't have been able to innovate and execute nearly as fast as they have.
As one of my Comp-E professors once quipped, "If a structural engineer ever tells you programming close to processors is easy, ask them how they'd like their job if the physical properties of lumber changed every 2 years."
Also, the game they were using to validate the performance of their hardware (Doom, I think?) ended up being so different from other software in how it used the GPU that their optimizations didn't really transfer.
I suppose some of the "DNA" lives on in AVX-512..