Rebranded GOG? Don't need existing customers? You are fucking crazy. Fallout from Sony basically closing GOG (only DRF free store on PC market and only place interested in keeping PC gaming history alive) would be bigger than anything we ever saw in gaming.
And you still missed that, but Sony has it's own working store. They don't need to launch new product or anything. They just need to extend it by adding PC games category to it and preparing launcher which would take care of licensing, GOG Galaxy is glorified download manager so it's no use for Sony if they want to use any form of DRM.
Even Techland was able to make their own platform which they shut down from lack of interest of gamers. Technical side of making online games store is not a problem for any company with semi competent IT team.
GOG is going to end up closing down at some point. There's a reason why they've already scaled back what games are on it. It loses money. Running a storefront isn't as easy as you think or transferrable. Like, oh we have PS Store, just put it on PC. You're clearly unaware of the work that would go into that. Oh, prepare a launcher, I'll put my nephew on it.
Making sure a multitude of games work and work well, the customer service element of it, which GOG currently has the best of, these are elements you get by buying CDPR on top of the game development.
Ask yourself if this is so easy, why Sony isn't selling God of War on PC through the PlayStation store.
It's on steam and epic game store though. Do you realize what a large cut Epic and Valve take? And they aren't selling it on PS Store at all... Because it's not as simple as you think. It takes time to ratchet that up and make sure it works properly and integrates within the current system without performance issues.
We're talking tens of millions of dollars, but what about Sony's semi-competent IT Team?