shouldn't be overly difficult - happy to accept a PR!

Here you go #1739

A related use case for a TypeScript keyword-spacing rule is this:

In our TypeScript codebase, we want to ban if(condition) in favor of if (condition). Enabling eslint "keyword-spacing": "error" will fail on code that does a type cast that involves this, for example
<unknown>this.property
because this is a keyword in eslint. However, we don't like
<unknown> this.property
with the space. Setting
"keyword-spacing": ["error", {"overrides": {"this": {"before": false}}}]
allows the type cast, but now comparisons like a > this.property fail.

Do you think your rule will be able do enforce this?

@rhuitl I had a look at it.
The problem is that I would have to overwrite the checkSpacingBefore function and therefore re declare pretty much every keyword's rule.
@bradzacher @G-Rath Is there a way to preventively suppress the expected reporting of a rule? It would be awesome to leave a dont report here flag for a subsequently-run rule. Without this, I don't think @rhuitl's request is doable without rewriting every single rule.

it is not possible, unless there's something in the base rule's code.
My recommendation is to never use angle bracket assertions anyways, as the syntax is easy to confuse with JSX, and will actively not work in a TSX file.

This is a separate case, and I would not worry about it with this issue @OoDeLally.
If it's important to @rhuitl, they can raise a separate issue for it.