You have asked this question in the past. Looking at that topic it seems like you’re one of the few people who actually have experience with deploying rspamd in Mail-in-a-Box 
I wonder how that went and if you’re willing to share the work via a pull request? The first requirement to get this into Mail-in-a-Box is for someone to do the work. It won’t happen by itself.
I think the maintainer is open to these kind of changes if they are well tested, give added value to the project and don’t burden him with additional maintenance tasks. Of course, don’t take my word, it would be best if he confirms this 
Update: oh wait, he did