That reasoning is over my paygrade, I don't know enough of EE design to even speculate. I think that you would want testing configuration to resemble final one in as many aspects as possible. That's why I would assume that if anything, they have been enhancing their CUs with RT tech. They started early, so it's possible that tech was still under development in AMD when they wanted devkits out. We still haven't got any RDNA 2.0 Navi, right? So probably they had to wait. So I would assume they build everything they could at the moment, including BC, to focus on CU changes and appropriate APIs later on. But that's also based on my personal opinion that 36 Navi CUs at high clocks is just a good idea. It made BC simpler, chip isn't that big, bandwidth improves with clocks. It would just fit with their usual pricepoint and give them enough juice to make jaws drop.
I said many times - I think XSX surprised everybody, because nobody thought it is a realistic target. Now everybody expects Sony to beat it, even though it is risky to abandon their market-proven strategy of hitting relatively low 400$. We are about to see the start of subscription wars. Sony wants to move a lot of units quickly, to ensure PSN strength during generation change. This is how they make money. Not by pleasing hardcore segment with tech sheets. As long as they deliver on games, hardcore players will quickly forget about the specs. Mass market will never forget about the price. Everybody agrees that if MS delivers XSX at 500$, they will also deliver Lockhart, for exactly the same reasons - 500$ machine is too expensive to quickly grab enough market to ensure strong position in subscription race. I don't think Sony is a fan of multiple SKUs, they probably feel it would diminish their brand, cost too much and only complicate things. Therefore, I strongly believe they will hit 400$, with all the consequences of that.
I also think Sony temporarily lost the narrative. While in my opinion their 400$ box stragegy would be way better than performance wars,now they are framed into this spiral of expectations. It will be quite hard for marketing to break out of that, but if their launch window lineup is good, they will manage. I also think that DF material might have been there precisely to let people slowly accept it as reality, so they don't feel too disappointed and rather hype on new, awesome games.