That's quite different. If A is crossbred to produce B, and B is crossbred to produce C, even if A and C cannot interbreed you won't accept C as a new species, because A and C can both interbreed with B.
Obviously, if I point out any man-made line of crossbreeding steps, each plant at each step can interbreed with those near it, so no example would ever qualify. And any naturally occuring line is invalid because you will accept no proof that any plant, such as coffea arabica, was actually derived from the source that I claim.
You realise that by this definition, you would consider A and C to be the same species, even if they can't interbreed! I suppose that makes as much sence as saying bison and cows are the same species...
We'll have to just let it go at this point. I have no idea what I could possibly offer you.
You are just trying to redefine a species as any number of things that can be interbred with any number of other things. This isn't what is being discussed. Look up the definition of species (closely realated subsets of species which all carry the same genetics as the overall species, just different dominances). You don't have the A, B, or C anyway.
You realise that by this definition, you would consider A and C to be the same species, even if they can't interbreed!
You're still engaging in a speculative fiction here. Living species are living species, not imaginary ones that live nowhere except in speculation. Just go out and demonstrate your hypotheitcal process with real living things and get legitimate biologists to classify the result as a new species. I will accept that.
Populate an island with male great Danes and female chihuahuas (or vice versa). Come back in 100 years. I'd be surprised to see any dogs at all.
Or populate the island with male and female of both breeds. In 100 years I'd expect to see two, true-breeding, populations.