Hello! As a forewarning, don’t expect me to do a good job catching up on this but feel free to reach out to me if I should follow up. But I felt the need to clarify one thing: the Racets talk was meant to be in contrast as a non-ocap approach that has an explosion of complexity around its code to handle access control that, if you read Jonathan Rees’s "Security Kernel based on the Lambda Calculus (though I can’t post since I’m a new user), you’ll see how much simpler things can be. The real a-ha is when you realize that the code for the ocap approach could be pretty much just all the normal programming code (scheme here, but Javascript is also possible; the Agoric folks are trying to enable the same things in js-land). It turns out that normal argument passing to functions, object methods, etc is our security model. We already had it, if we took it seriously!
I’m happy that in ActivityPub we achieved a lot of interop availbility through Linked Data Notifications. I’ll admit though, the main reason I haven’t paid much attention to SOLID is because it has an ACL approach. I’m confident that this will hold SOLID back from its lofty and honestly really thrilling goals. And I’m a linked data fan… there’s a reason that AP is also linked data 
It took a long time, and research, for me to come to the conclusion that I couldn’t do the kinds of things I wanted to do in Spritely with an ACL approach and that an ocap approach was necessary. I think an ocap approach could compose nicely with SOLID, and I vaguely read that the SAFE on SOLID approach is doing so though I haven’t honestly fully followed it…
I’m semi-happy to discuss further, but I’m also very busy; I’m interested more in discussing really if the SOLID core developers are interested. If not that’s totally cool and I wish the SOLID project well