Sony is not in the position to eat the cost of anything, their margins are tight already
This is false; they can eat the margins, the high-suit executives and CEOs just don't want to because they want more money lined in their pockets.
The way the console gaming business has always been structured is, you take a small hit on hardware sales or just have thin profit margins, but make the majority of your profits through B2P software sales and, nowadays, subscriptions, MTXs, etc.
That's also been one of the main reasons consoles have been able to stave off attempts by idiotic regulators to become open platforms and have competing storefronts on them. When your business model mainly relies on subsidizing the hardware (to get it to as many millions as possible) and recouping the costs on other things (including peripherals), you have a solid case as the platform holder to retain a closed platform where you retain full vertical integration.
So if Sony are going to pursue a model going forward where they push for huge profit margins on hardware, no longer subsidize the costs, then they shouldn't be surprised if and when regulatory bodies force them to allow alternate storefronts on PlayStation consoles. Because they won't have the excuse of the traditional model anymore to back them up, especially with hardware costing in the territory of mid-range PCs (especially once you factor in the costs for PS+ and typical game prices over the gen).
Nintendo would still be safe from that type of forced action because they can leverage the fact the majority of game sales on their hardware is their own software, but Sony never had that luxury, therein regulators would tell them to consider what's best for 3P and push the open platform policy unto them. Microsoft will just try getting ahead of it by making Xbox essentially a PC in the business model, but probably tie access to alternate storefronts to some Game Pass tier to try leveraging Game Pass as a means of pseudo-subsidization. Sony could technically try for similar by tying alternative storefront access to a PS+ subscription, but this is where the kicker comes in.
See, all of the alternative storefronts have Windows versions, so all MS really has to do is add extensions to Xbox OS to run the Windows code those storefronts need, on Xbox hardware and that's a large part of the work done. They wouldn't really need, say, Valve, to make a specific Steam app for Xbox. Sony, OTOH, don't have an OS where these other storefronts are already available. Meaning, they'd have to get Valve, Epic, GOG etc. to make builds for their OS, incurring additional time and costs on those companies. They would most likely take up the task due to potential money from PlayStation customers, but it'd still require more work vs. the Microsoft approach.
So on paper both Sony & Microsoft could have similar alternative storefronts with a similar means of access tied to them (subscription tie-in), but then Sony are still at a disadvantage because taking this more open-platform route means Microsoft can also leverage Windows apps to run on Xbox devices, and there are a LOT of Windows apps for entertainment, productivity, business etc. Now is that type of functionality extended to Xbox going to appeal to a wide assortment of gamers? Potentially no. But there are niches who will be interested in those. Sony has no OS in the PC space where there's a vast network of applications to pull from, but they do make some productivity software on Windows. In theory, then, they could just build ports of that software for the PlayStation OS and provide them potentially as perks to various PS+ subscription tiers.
Also worth noting, if that future is pushed onto console makers, they will probably also be "forced" to get rid of paid online. Not because regulators demand it, but because it'd just be a bad look for them to still require paid online locked behind a subscription paywall when taking on a more PC-like business model, knowing online is free on PC.
