[moonchild]

Typing symbols is not really an issue. First off, you can configure your text editing environment to automatically replace digraphs with their associated symbols (e.g. when you type i. replace it with ⍳ automatically). But second of all, memorizing an alternate keyboard layout isn't that big of a deal. Is it really harder to remember that grade up is super+shift+4 (⍋) than that it's slash+shift+; (/:)?

I would argue that difficulty in reading code and knowing what symbols represent what operations is a much more pertinent consideration. And though neither is especially mnemonic (can you really have a mnemonic for something as abstract as 'sort'?), it's much clearer that single-character grade down (⍒) is the reverse of single-character grade up (⍋), than for digraphs (/: and \:). (It's also easier to parse symbols when they're only one character.) Not least because unqualified / and \ represent very different operations—the first is reduce, and the second is either scan or prefix—as do /. and \.; so there's no precedent for it.

And so, assuming you accept the obvious superiority of graphical/unicode representation of symbols, the digraph method for typing them becomes superfluous. You now have to associate the mental concept of grade with two completely separate representations: the graphical representation of the completed character (⍋) and the ascii representation which you type (/:). You can't escape the latter, because every time you type a grade, you'll see the '/' on screen for a moment before you type the ':' and the character gets digraphed.

I mentioned in the beginning that you can configure your editor (and repl) to automatically replace digraphs with their associated symbols (so /: automatically gets replaced with ⍋). On face, this seems functionally equivalent to the ligature suggestion, but it's not. Mainly, it affords flexibility. If you want to type digraphs in your environment, you can, all my criticisms aside. But I can configure my environment to use an alternate keyboard layout, avoid complicating my editor environment by introducing ligatures, and we can work together seamlessly. Doing it that way also adds flexibility to the language; if ⍋ is the single canonical representation of 'grade up', and / and : are separate symbols with their own unique semantics, then they can be freely juxtaposed. It'd also be somewhat of a pointless indirection, to have ascii digraphs underlying what are essentially unicode-pictorial representations.

(Note: I said only 'digraphs', for clarity, but everything I said applies also to trigraphs, of which j has a couple.)

[yiyus]

It looks to me like you see no difference between "I need to configure my environment" and "my environment is already configured by default". But, from my point of view, the difference is very important.

I like being able to type some J (or, most times, some K) in an email, in a note I take in my phone, in a comment of a C program, ... Yes, I could configure my environment(s) to do all this with a custom input method, but being able to do it with anything I find without any configuration is a huge advantage.