What aspects of the language are you convinced cannot be optimised? There's tons of research in this area.
> mutable interpreter frames, global interpreter locks, shared global state, type slots
On top of this, Python is extremely dynamic and nothing can be assured without running through the code. So this leads to needing JITs to improve performance which then give a slow start up time and increased complexity. Even with JIT, Python is just not fast thanks to the above issues and it's overall dynamism.
It can be optimised and for sure there's some impressive attempts at doing so. However I don't think pure Python will ever be considered "fast" as these things necessarily get in the way.
I highly recommend the two videos posted here that go into more detail as to why there are limits to how far optimisation can go: https://youtu.be/qCGofLIzX6g https://youtu.be/IeSu_odkI5I
I'd challenge the idea that there really are known 'limits'. As I say there's research towards this, these videos are old, and Armin and Seth may not be up to date with all of the literature (in fact I'm sure Seth is not, as he's missing at least one major current Python implementation research project from his blog post.)
There are good reasons why these limits cannot be overcome in that the complexity and dynamism of the language precludes it.
Being interpreted is one cost that sets a significant barrier to performance, and the dynamic complexity further compounds it. For example whereas JS is basically only functions, in Python you have a huge range of ways you can do incredibly complex things with slot wrappers, descriptors, and metaprogramming.
Ultimately, Python will get faster, but diminishing returns are inevitable. Python can never be as fast as the equivalent code in a compiled language. It simply has too much extra work to do.
Having the option to be slow startup/fast execution is a good option to have. Maybe not for some, but definitely needed by others.
These are only simple benchmarks, but do indicate a rough ballpark for TruffleRuby: https://github.com/kostya/benchmarks
As I understand it, Crystal would be a good Ruby alternative if you want performance. This is of course a whole new language designed with performance in mind from the beginning and here is a repeating theme: you need to consider performance at the start, not 20 years later.
