My article for this past Shabbos in The Jewish Link was about the importance of teaching dikduk, as well as linguistic knowledge more broadly, applied to languages such as English or Italian. Students should know phonology in general so that they have the intuition and capabilities of tackling Hebrew
So, for nominative vs. accusative, this can be described simply as "I" vs. "me". Understanding that I is used as the subject (I ate) while me is used as the object (She spoke to me) is useful for speaking English correctly. If taught as part of a general curriculum of linguistics, people could internalize it and not use the nominative case all the time when joined with another actor, like they do in all TV shows. "She spoke to Bobby and I".
When it comes to Hebrew, distinguishing between the nominative and accusative pronouns may now make more sense. After we encounter accusative case endings in languages like Turkish (Araba as nominative for car, Arabayı as accusative case), we can maybe recognize that the Hebrew word "et" is the accusative case marker. You can tell students this, and they have an English / scientific term to tap into. Instead of saying "et" appears (sometimes, not always) on the nouns that things are done to.
I don't know that knowing dikduk Rashis will help for Hebrew linguistics. But the broad knowledge will both allow people to approach the dikduk Rashis, and to approach even modern Semitic grammar.
Important topic. Comments on the following, I added numbers:
>1) But more than that, grammatical ignorance isn’t restricted to Hebrew. Ask these students if they can provide an example of an English subjunctive. Can they distinguish between the English nominative and accusative pronouns, between a sibilant and a dental or between the active and the passive?
>2) People skip the dikduk Rashis—not just because they don’t know dikduk—but because they don’t know how grammar works and lack the vocabulary to discuss it.
1) I'm highly interested in linguistics, and I've spent probably hundreds of hours on my own studying it. And yet, I wouldn't necessarily be able to provide examples of the terms you mention. To give a coding analogy: what you describe is akin to "white-boarding". Off-hand knowledge of technical terms isn't especially important, IMO. To be more concrete, I'd say it's important to know what a pronoun is, but less important to know off-hand the difference between nominative and accusative. Those terms are just difficult to retain, and it's not realistic, nor especially important, for the average motivated individual to remember them. Of course, it is different if one is particularly interested or are currently researching that specific linguistic topic (see my recent piece on part-of-speech tagging of Talmudic text).
Ultimately, as you hint to in the end (and as with coding), what's important is "getting a feel for the language", and less so memorizing all the technical terminology. This is especially the case with the ready access nowadays to ChatGPT, Wikipedia, etc. Of course, basic knowledge is still important, I'm simply pushing back at how detailed the off-hand knowledge of specific technical terms is.
2) I haven't looked into it especially, but my understanding is that rashi's dikduk is somewhat foreign to the modern linguistic model of Hebrew (especially in terms of the modern standard model's assumption of triliteral roots, in Semitic languages; taught in all Israeli schools). So I'm not sure that understanding Rashi is a good metric for a proper grounding in Hebrew linguistics .