Whilst this is likely, unless we know of anything different with this PS4, then the XB1S has a chance to still sell better given it's 4K ability for streaming blu-ray playback etc. If the PS4 is still stuck at 1080 then they are missing a trick in my opinion.
You can do 4K streaming on your 4K smart TV without buying a 300$ separate box.
UHD BR is a very small business. People actually interested are a niche within the niche of 4K contents. Tons of people even today don't even care about standard BR movies, go figure UHD.
It's nice that MS can offer those things as a plus in the entry level model but realistically the market appeal of those features right now is very limited. It's pretty much like claiming that backwards compatibility would change the market situation. People who actually consider that a selling point are a small group.
A PS4 Slim at 299$ (plus deals) will sell a LOT in the mainstream market. And on top of that they'll also get all the Neo sales from upgraders and people who actually care about 4K.
Sony is really well positioned this holiday season, there's a reason they are forecasting 20m units for the fy.