I am a developer of iSH; tbodt did most of the interpreter work though. (Actually, he did most of the work on the app in general–there's a couple more of us who dabble in other parts of development, as well as support, marketing, compliance.) We're glad you like the project :)

Getting iSH on the App Store did take some work on our side; we were in contact with Apple to get it approved and in compliance with the guidelines. You may have seen that the version of iSH on the App Store had package management functionality removed. So far we've been able to keep the ability to run Linux programs, as well as import files, unchanged.

One interesting thing to see from Apple is that they are not just increasing the performance of their chips, but they are investing heavily in making certain operations faster. For example, in the time since tbodt started working iSH Apple has reduced the cost of uncontended atomics to almost zero overhead (this is especially good for Apple because it immediately makes reference counting code faster, which both Swift and Objective-C spend a lot of time in). iSH doesn't currently do anything fancy there, it just uses full locks everywhere, so this is something that we would be interested in pursuing at some point.

Faster uncontended atomics should improve uncontended lock performance too, at least if you’re using pthread mutexes (they’re implemented via atomic operations with an os_unfair_lock fallback for the contended case on Apple platforms).