Bottom line: I wouldn’t expect many discounts here.
Plenty of them already do. Google's services (YouTube Premium and others), for example, are $5/mo more expensive if you purchase them via Apple IAP. Spotify memberships are 30% more expensive on Apple. There are countless other examples. They just weren't allowed to advertise the cheaper option on iOS until now.
Even if a particular list price doesn’t change, I’d expect more frequent and deeper sales.
In a less competitive market for a good or service (due to lack of antitrust enforcement) there should still be discounts, in proportion to the residual competitiveness. E.g. the mobile game market is very competitive, so I’d expect more discounts vs. the video entertainment market where there has been a lot of aggregation.
I've also heard Netflix has suspended all in app subscriptions and is only going to link to their website for sign ups. I'm unsure if that will translate into savings, but I suspect you're going to see more of this behavior as well.
The 30% / 15% tax is very real and companies that don't have to pay that will be better positioned in the long run, so I imagine even if the price is the same, they'll be able to pocket more revenue doing this as well
I suspect this won't affect games much, except for the exceedingly big ones like Fortnite, but I treat that as a whole separate sector at this point.