Isn't "crippling" a bit excessive? Something like 10-12TF of performance seems a reasonable expectation, based on assumed die sizes for a console and the known die size of the M160. We'll have to see what performance it reaches at lower clockspeeds before we have a clear indication of an approximation of performance at console wattage, but the current performance of 14.8TF for a GPU that was meant as a 7nm pipe cleaner bodes well IMO. We'll have to wait and see, but hopefully there's truth to the reports of some Zen engineers moving over to work on Navi, and hopefully that pays off in the form of improved perf/watt.
But let's be conservative and assume a 10TF GPU, which can have any ratio of performance dedicated to rasterisation, ML, and RT. Would that flexibility really hamper it so much?
I can imagine that all 3 might be somewhat compromised, relative to fixed function hardware, but does the penalty to performance still result in a functional RTRT GPU? To my knowledge, that's an unknown.
Does the penalty to the size of the CU's outweigh just having fixed function hardware? The M160 suggests that AMD might think so.
And if the answer to both of those is yes, does it make it any cheaper to manufacture? Potentially so, if AMD are able to just deploy different amounts of differently clocked multi function CU's to satisfy all of their markets.
RTRT is still nascent in gaming, but it can't hurt to have the entire core gaming industry beavering away on solutions to it. It'll just be the way it always is: lower quality on the consoles.
And if any developers don't want to, that's fine, they can act as if they have a 10TF PS4/XB1 with plenty more memory and a way better CPU.
Edit: I also think it's worth mentioning that Sony's new CEO mentioned ease of manufacturing as key for the PS5 - I'll try to find the source. Considering "ease of manufacturing," AMD's recent chiplet Zen 2 design, their continued push for Infinity Fabric, and their multi purpose CU's, I'm convinced that, if the CU's can be modified to be capable of RT, that's the approach AMD would want to take regardless of developer convenience.