- Negation. This is just an adverb in Scandinavian. The slightly non-trivial thing is that the position of this adverb (also some others) is different, depending on whether it's a main or a subordinate clause.
- Lexically reflexive pronouns. As in Romance, some Scandinavian verbs subcategorize for lexically reflexive pronouns, which have no semantic value.
- Lexical passive. Scandinavian verbs have a lexical passive form. I propose to do this in the morphotax.
- Definiteness. I don't yet have all the definiteness constraints. In particular, a definite singular NP has an implicit definite article, but a premodifying adjective requires an explicit definite article.
I don't think any of these things are particularly difficult to implement, or should require major changes to the grammar.