OK, that clears things up; I thought they would conflict, or experimental-modularity would override SIP-64 changes.
I thought that because of the as keyword I see in the SIP-64 changes mentioned here, which was discussed in the pre-SIP discussion, and I was under the impression that as was decided against (I was involved in that discussion)… But I think I’m confusing as for context bounds with as for named givens. 
One more confusion is that this (which I thought was more “up-to-date”) seems different than this. But now I understand that they are related but separate (one is a follow-up to the other).
I’m still confused, I’ll probably wait until 3.7 for the dust to settle to fully understand it.