yea, in the future games might come on USB sticks or sth for the physical collectors, as I doubt PS6 gen will have an optical drive

I think this is very possible in the future.  Optical drives are big, and have a lot of moving parts that are prone to problems.  But, right now, disks are a lot cheaper to produce than flash memory (and the like).  That will change at some point.

Absolutely one of my biggest fears about a digital-only future

There is 0% chance the next generation doesn't have a media drive. Blueray capabilities are still far too important for entertainment. Forget about games, and look else where. It's still an essential piece, and I don't see that dissipating in the next 10 years even.

There will be still competition between the games themselves, even if there is only one store. They will continue to offer games in sales for reduced prices after a few months and frequently in the following years.

Just look in the iOS AppStore or games with mandatory Steam DRM... the next sale is just around the corner.

And if I'm wrong... well, my backlog of good games should be enough for three lifetimes.

Cause i'd like to pay less for games and being a monopoly on selling them gives them less incentive to cut those prices?

That won't happen for decades. It doesn't help that games are increasing in size faster than hard drives can keep up. I won't be surprised if 100GB games are for 9th generation consoles(AAA games only). Also, physical media will have a market too big to ignore. Nobody is going to abandon that market anytime soon.

At best you'll see a PSP Go style console as an optional model.

Physical will definitely still exist next-gen, but with every new major release we are seeing a larger percentage of sales coming from digital.

Honestly, I'm pretty sure I'll be going all digital next-gen as well.

Too early to replace physical media already next gen. ON PS4 digital sales just reach around 50%, the physical media will not be dropped before digital is at least 80%, probably even 90%. And even then console makers have a problem: the retail needs to list these consoles. If a console manufacturer decides to drop physical media the retailers will not be very happy and may decide to delist the console too.

Next gen is way too close for this to happen just yet