I wish a language was designed to allow identifier with space in them without quotes. That is the most readable. But I don’t know the consequences to the rest of the grammar
The obvious solution would appear to be to use better keyboards, but I don't even see anyone suggesting that.
But note that the lisp identifier style, words-separated-by-hyphens, is better than using underscores despite being less legible. It's purely a matter of how easy it is to type the separator. ("Standard" languages don't allow hyphens in identifier names because they want to allow subtraction without requiring a space between the subtraction operator - and the two operands. In Lisp, spacing around an operator, including the subtraction operator, is required. You could go a long way in a C-like language by just requiring spacing around operators and immediately being able to allow hyphens in identifiers.)
Shift key is a problem for all the shifted only chars. Their major problem is appearance: a single underscore '_' vs underscores '__' . Concatenated glyphs are hard to discern due to only distinguisher being width.
We have various natural languages to tell us: https://en.wikipedia.org/wiki/Syntactic_ambiguity