I believe this is pretty doable to be honest because when you’re going from an approach of teaching grammar, you need to know where the questions come from. That’s where you need to use SRS.
Simply put, the solution is about turning an usual workbook into SRS. Another problem with textbooks is that they might lack important information the student should know about. I assume this lack of information exists because either they don’t want the students to become overwhelmed or they lack the knowledge to know which information is relevant.
Another thing is establishing rules. A student can easily binge on grammar and not learn things right. This happens for several reasons, but most people don’t know their limits in terms of retaining information or they don’t know how to study (a language). Simple things like “this textbook was designed so that you study 1 grammar point per day during an year and achieve x” (kinda like how Wanikani works) can change the game.
In terms of order of material, I do think following the JLPT order can hurt in the long term. Sure, going in a JLPT order might seem attractive, but there are grammar points considered to be at different JLPT levels that should be taught together.
I’m writing a textbook as I go along learning Japanese and this is pretty much what I noticed. Trying to teach while being the student has its benefits in my opinion. But again, just my 2c xD