I dont think Alan Wake is a "big exclusive" by any means. 

I wouldn't buy it if it came to ps4, looks rubbish to me :/

Whether it does or doesn't shouldn't really matter to ether one anymore. Xbox is now Big enough it doesn't really need it anymore and Gears isn't as big a pull as it was and PS has Uncharted now that's as big or bigger than Gears.

I really like Xbox and as a fan I think it might be not that bad if Gears goes multiplattform this time.
If Gears goes multiplattform MS finally has to invest way more in own IPs from their 1st party studios, they cant rely only on Gears and Halo to get core gamers on their system than all the time anymore.

Microsoft has has to crate anyways many new IPs and games next gen, so if gears go multi it only will compel them even more to create new IPs.

it would certainly be a dagger to MS reputation

FF13-2 on the PS3 sold more than the 360 Version of the extremely overhyped FF13(cause everyone believed they get a FF7 with HD possibilities so everyone wanted it).And it had the drive of the strong numbers of the 360 in the USA...Everyone was like "OMG Sony is doomed...Microsoft stole their big Franchise!!!"
Yeah - 5-6 years later no one cares cause SquareENix sucks anyway...
And FF13-2(PS3) was already affected by the letdown FF13 was and still sold more than the 360 Version of FF13.
That is a good indicator.
Gears wouldn't sell as much on the PS4 of course but the gap wouldn't be as big.It could get a big boost in Europe and Japan and the PS4 will be the number 1 choice on the gaming market so the possibility is given that the PS4 is closer in numbers to the NextBox in the USA > More sales there too.

I think Gears Judgement is just doing so bad compared to the other games cause it isn't with the maincast of Fenix and Dom and made by a different developer.
Its a spinoff as much as it can be - A last money grab in this Gen with the Big Name the franchise has in the community combined with the only "Big Name Exclusive" on the 360 in 2013.Probably just to show the console isn't completely ignored by developers even if its just another game of a overused franchise.

And i really don't care anyway.Even if Gears comes to PC with completely outmaxed Unreal Engine 4.
I think the series is completely boring and just did so well cause it did hit the "Gore" taste of the community in that time.

But the Japanese Xbox install base was so low it still wouldn't have made a difference. Look at Monster Hunter Frontier. Granted it a spin-off, but thats a very popular series in Japan and VGChatz number say it sold only 130k units.

On-topic: Microsoft won't want to lose Gears as its such a major exclusive and EPIC enjoy working with them (apparently). That said, I can't see how they would take the series forward after Gears 3 after the Locust were wiped out. That means the series is restricted to prequels, spin-offs remakes that limit its creative scope given that the canon after said new game is fixed. So personally feel Gears is past its peak.

they can think of sumthin

Why do people think Gears will continue? They stopped with new books because their is no future in the franchise. Now the comics are also also going to an end. It looks like it is over like possible other franchises.

i hope so, because you know what they say:

"Gears? Possible and the only xbox exclusive worthy of a meltdown"