Why would you want to replace Lua in this space? At least why replace with another dynamically typed, imperative scripting language, but without tail-call optimization? What would be the gain?
I'd also like a language that puts more emphasis on backwards-compatibility than Lua. Sure, everyone complains about the Python 2 => 3 transition, but there have been 3 new major versions of Lua since the release of Python 3.
The crowd of people who speak Lua is pretty different than those who speak Python.
I would guess the Lua crowd to be older, more experienced, but smaller.
The Python crowd is much bigger, and includes people who dabble in coding rather than those of us who do it for a living.
It depends on the user base of your application, but I can totally see why Python would be a better embedding language for users to use. You build the product for the users after all.
In todays world, I'd make some V8 bindings and get users to use javascript, because that's even easier to embed, has a bigger ecosystem via nodejs/npm, and has a probably larger userbase... It's got a nice remote debugger/UI too, which is quite a plus if you're expecting inexperienced users to write plugins/modules for you.
The only other implementation that really supports it is PyPy which is not in any sense more lightweight.