You do realize how much money they would lose at those prices, right? The bill of materials for PS5 is rumored to be in the upper $400's range, with Sony possibly still losing some money selling PS5 at $500 after the cost of shipping and the retailer cut is factored in. But for the purposes of illustration, let's say they break even selling at $500. That'd be a $100 loss per console selling the disc drive version at $400, say they sell 5m of them before costs start to go down, that is $500m lost. Digital PS5 meanwhile saves them about $20 on the disc-drive and maybe $10 on the SSD, so they'd be selling a $170 loss at $300, say they sell 20m at that price before costs start to go down, that is a $3.4b loss. Sure they can offset some of that loss with the increased profit margin on digital games and subscriptions, but that's still alot of money lost even then.
Far more likely we will get either $500 disc drive/$400 digital or $500 disc drive/$450 digital imo.
My comment is solely based off of how vicious Sony is regarding hardware pricing, sans PS3 of course. I think they want to undercut Xbox even if the losses will be great. Let's just wait and see what happens. I'm not an insider, just thought this would be interesting and if they'd consider doing that. Of course this all relies on how much of a loss Sony wants to take. But like Trunkswd said, a digital at $399 does seem more feasible if Sony wants to keep a $399 system on the market.