This thought was sparked by Watch Dogs numbers, with the PS4 doing obviously better than the X1 and third party games thus doing better on it as well (especially with the right marketing ;)), could it become better for medium/small developers to just make their games exclusive to PS4, if the generation continues on the way it's doing right now?

For the big developers that expect to sell millions of copies of their games, it'll always be smart to release on both platforms, but if you're a smaller team an maybe only expect your game to sell 1,5 million, why not just go PS4 exclusive?

Some advantages of this would be:

Porting obviously takes resources, those resources could instead be used to work on something else if the game was on only one platform. The Devs could put more manpower into making the game better or just have it be done faster, which would lower its development costs.

Exclusives generally get an attention and hype bonus (e.g. that russian PS4 exclusive that nobody would've ever mentioned if it wasn't going to be exclusive). Also Sony would possibly be willing to carry some marketing costs for exclusive games from third parties as well.

The big disadvantage would of course be the loss of a still very big audience, but for smaller games that could probably be balanced out by the advantages I listed.

So do you think that we might see some more third party exclusives for the PS4, if the gen continues like it started?

Hopefully, that will make my investment an even better choice.

well wouldnt it be easier to make a pc version then port it to x1 in i think has been is like 4 to 5 months and then you have 2 games if they use dx12 i belive 

Watchdogs has exclusive content on PS. If you can see this pattern for different multiplats, you would have a case.

Also, even if it sells best on one platform, other platforms can be profitable, if they reach a threshold of sales. How much probably depends of a lot of factors, but usually some 100K should be enough to make a port profitable.

That's not the point. The point is: Could smaller games be more profitable, if they just stayed PS4 exclusive instead of going multiplat?

Well they could but they'd lose out on the X1 audience which is still makes up a significant amount of the market. If the PS4 can take 70% of this gen's marketshare than I agree that developers shouldn't bother making their games for other systems.

AA : Yes
AAA: Probably no.

But AA's will have to make a resurgence for this to happen. I expect indies to become the new AAs late 2014, Early 2014

Doubt it especially for bigger 3rd parties, as porting between the platforms and PC should be quick and easy enough to cover the cost and make a hefty profit.
What this warrants though (at least I think) is that no multiplat will skip the PS4 if not moneyhatted and smaller developers which usually preferred X360 last gen and often skipped PS3 may now choose PS4 over X1. We have a few examples already.
Also hopefully developers will choose PS4 as the leading platform and then downport to the Xbone, not the other way around, securing the best possible experience for the biggest amount of gamers.

Because of their parity clause I can see plenty of developers skipping X1 cause they don't have the time and money to ensure parity to release on both simultaneously.

Especially for AA titles that have a greater Japan/Europe or worldwide appeal. Given a similar size of the "core" gamer market and the pace at which the PS4 continually outsells Xbox One, the Xbox One will be lucky to get half the sales of the 360 in its lifetime.