I just want to call out that Akka doesn't require you only interopt between services also using Akka. If it did, it'd lose quite a lot of the benefits you want

I just want to call out that Akka doesn't require you only interopt between services also using Akka. If it did, it'd lose quite a lot of the benefits you want to get out of an Actor library. In truth, to interopt or not is a decision the developers make and it's also a decision they can (should) un-make.