I think the key is to buy the new body along with whatever your "next lens" purchase was going to be. Then slowly switch over. It takes time. There's nothing wrong with owning two systems, especially if you segment the use cases somewhat. I've owned 3 or 4 different systems at the same time in the past. It keeps life interesting.
Still, given how spoilt I am

changing systems is an expensive proposition. Just going through a migration Hasselblad H -> Hasselblad X and it is painful, financially

. I do love the new toys

Counting pure ILC's (i.e. not drones, action cameras or phone cameras) I have 2 systems: FF 35mm (R5) and crop MF (X2D II 100c).
That's me sorted... more systems also means more types of accessories (batteries, memory cards, flashes, etc.) and, honestly, I do not shoot enough to justify more than I have....
There are no rumors of a 105/2, but Sigma pretty clearly wants to keep doing things to elevate themselves above the Chinese makers, and they definitely want to be the go-to for astro glass. The 105/1.4 was a big deal when it came out and was a big (literally and figuratively) halo lens for Sigma at the time. Since they already have a 135/1.4, if they're going to bring out a 105 I think it will be faster. With that in mind, I'd be shocked if they weren't at least considering (and probably prototyping) a 105/1.2.
I figured, but I was facetiously serious: with me being into portraiture / fashion and me loving more teles over wides, it means I'd be truly intrigued by a lens such as the 105/1.2... and given the other interesting Sigma lenses available for L mount and Sony... pity if I had to choose a mount from scratch right now it'd probably be Nikon

but no FF Sigma for them too