It took a ton of consideration when I bought the 70-200 is mkii... and that was two grand. I can't see a future where I pay 4 grand for a lens.
Would I consider paying a premium for a lens that is in the top of its class, but I think two grand is where that willingness starts to die out.
I was in the same boat... but now i'm considering a 300 f/2.8... situations and priorities change. I am fortunate to be in a good financial situation, so it is plausible... several years a go when i finished my PhD and didn't have to pennies to rub together, buying the 55-250 was a monumental decision! Never say never! I am also looking at it as an investment. I can always sell it if i come into hard times.
Saying that, i've still got to save up for it and then pluck up the courage to buy a lens instead of a used car (or 3 new Royal Enfield motorbikes)...