AMD is going to use a huge amount of cream-of-the-crop Epyc chips for this bad boy alone and, if we apply the "rule" of only the best 5% of chiplets go to Epyc and only the best of those goes to the top chip, than that's a heck of allot "not good enough" 8c chiplets after the binning process.
I'm pretty sure initial yields are much less ... shall we say ... favorable ... then AMD would have us believe, simply because it's a new process. This will ofc improve with time and then it's quite possible AMD will end up sacrificing perfectly good chips for lower solutions, depending on the needs.
I expect it to happen right away personally. But it will probably be tiered. There will always be the issue of cheaper processors selling in more volume. I think it's a while before AMD disables an 8c chiplet down to 2 or even 4 cores. But I expect most of the chips on a 4c Ryzen to be made up of 2 probably 4+ core capable dies, 6c CPU's with again 4c+ dies, 8 for 6c+ capbable dies 10 and 12 with 8c capable dies.