The smaller market share of the XB1 is primarily made up of core Xbox fans, most of which are adults with disposable income. I'm sure the majority will be quite happy to move on to a much better machine, and that's what Microsoft will want.
They aren't going to put the effort into releasing a machine with a 6TF GPU, better CPU and RAM, only to hamstring it by having to stay in line with a product that has cost them dearly.
Designing Halo 6 around the XB1 when you have this new beastly Xbox to work with? Please.
The XB1 slim will serve as an interim product to keep them ticking over until Scorpio's launch. Then afterwards be a cheap alternative to play the back catalogue and new games like COD, FIFA and Indies. As usual. They aren't going to sell a boat load of them at any price, not when there's 4+ better alternatives out there in Scorpio, Neo, PS4 and NX.
I could of course be wrong but I doubt it.