Not really. It will require no more than a 10% or maybe 20% increase in development costs to make a game available on PC, PS4 and XBO. This is because the core code that the game is made with can effectively run on all three platforms barring small changes to accommodate platform specific APIs due to how similar they all are. From a development standpoint, PC is basically Ultra settings (or everything else), PS4 is high settings and XBO is Medium.

If you see devs opting for PS4/PC exclusive development, it will primarily be due to MS parity clause (which i expect they will soon change maybe even as early as this E3 since they have changed almost everything so far and its arguably one of the most stupid policies they have). As is right now, a developer can just make their game for the PC knowing fulley well that in a month they can have the same game running on the PS4. But with the XBO, if that game has already been released on the PC/PS4 they can't release it on it, unless they hold back release of everything else so it can be released on XBO same day and date.

According to the consensus last gen it tacks on %10 to the cost of the game for one system. Now that number may have gone up due to current gen costs or down due to the fact that the 2 consoles are nearly identical.

I cant imagine this happening unless X1 sells less than 20 million LTD. If you can get a game that sells to %5 of the userbase its still 1 million sales which is a decent chunk of money.

edit: Also DX12 is apparantly going to make coding games for X1/PC much more seamless, so you are basically getting 2 versions out there for the cost of one. Unlikely to happen

Its timed. 6 months. After then it will come to other platforms.

Why would it be? One smartphone game pulls in the revenue that entire corporation do.

It's no harder to port it to PS4 lol.  It uses Open CL which is close enough considering double the install base and easier to utilize hardware.  Nice try though lol.

from the small developers we have seen probably a hundred+ timed exclusives out/announced already.

..but it has less to do with profit and more to do with resources. even a moderately big team like super big games or jonathan blows team can't really manage platform parity across all platforms just because they don't have the man power. transistor will eventually come to xbone. the witness will eventually come to xbone. most of the other best indies like octodad, don't starve, outlast, mercenary kings, towerfall, axiom verge will eventually come to xbone but these developers can't seem to support both at once and sony leads the market both in sales and in respect for indie developers.

multiplat will always be more profitable.

the small teams that don't go multiplat are the ones that failed and can't afford the additional development to make a port. ...or MS gives the finger to by enforcing the parity clause.

Gaming is practically irrelevant to smartphone sales, there is zero point to being exclusive to mobiles, you will only lose money that way. 

i'm pretty sure that it's a relatively easy task to develop mulitplats between xbox one and ps4.
if you just stick with a standard game engine like unity or unreal engine and don't optimize your code to a specific platform i guess you won't have much trouble.
i mean, we will see less of these console exclusive indies if microsoft banishes their 'first on xbox'-clause.

Looking at all the exclusive indie games I'd almost say yes.