Without wanting to derail the conversation about Language Servers, which has a lot of excellent points made by @GwynethLlewelyn, these do not actually provide much at the most basic level of editor functionality (e.g. highlighting, selection etc.) in Nova.
I think what would help for the issue brought up here, and in many similar scenarios like highlighting TODOs, links etc., would be for Nova to provide a way to inject features into existing syntaxes. Currently, a syntax can include parts or all of another known syntax (like CSS / JS / PHP in HTML, or Markdown code blocks), but if you want to inject some new syntax elements into a pre-existing syntax, your only way is declaring a new language mode and either clone the original syntax, or use Template Scopes, which lack any kind of granularity (for instance, you cannot restrict them to specific scopes, e.g. comments for TODO highlighting).
With such a feature, additive syntax extensions providing just that that bit of extra functionality would be low hanging fruit; without it, the onus is on Panic, and, by extension, more or less exclusively on @logan, to provide all syntax functionality. Which is very much not a sustainable state of things.