Of course it depends on your use case, in some cases a compact byte array performs better anyway, for instance because now you're able to fit it in your CPU cache.

What you're doing here is pretty cool, I think I will start doing so, too. I have a number of places where I use "undefined" instead. (The "undefined" from the Clash Prelude, which translates into a "don't care" signal state.)

But being outside of the mainstream may mean you need to occasionally debug more esoteric stuff: https://gallium.inria.fr/blog/intel-skylake-bug/ I'm sure Jane Street can afford doing that, but I'm not so sure if a small team can.

Because despite them being very open about it, no one else does it, and every distinguished engineer who pushes a weird tech choice will justify and defend it.

However, I very much disagree with Graham's 2004 assertion[0]:

  It's a lot of work to learn a new programming language. And 
  people don't learn Python because it will get them a job; 
  they learn it because they genuinely like to program and 
  aren't satisfied with the languages they already know.

I was a professional software engineer in 2004, when the Graham post was written. To say, "people don't learn Python because it will get them a job ..." was bullshit then just as it is now. The remainder of the quoted sentence is unfounded extrapolation and has the value of same.

0 - https://www.paulgraham.com/pypar.html