the new Vega card should come out in late december/early january, that is all that is known.
Be it 490 or 590 or whatever.
If it beats 1080 like AMD claims it does (by how much? who knows.. driver optimization and all such and... so far only AMD has been testing it, Will it hold same in 3rd party tests too?) it will lower 1080 price, I think.
1080 Ti performance is still also in air but.. if new AMD toy competes with 1080 and beats it, yes.. I think it would also cause pressure on Ti price.
Since no AMD or 1080 Ti performance/price is known at the moment, it is all just speculation