I am interested in motives. I think the search for truth (including moral-aesthetic truth) should be a primary motive.

Can we expect anything beyond internal consistency from philosophy? If not, then the philosophical project seems to reduce to determining when two philosophies are isomorphic. Some philosophers might argue that we cannot expect more than internal consistency in any field, but I think I've given a counterexample to that.

Of course, I think truth is more than a value we assign to a proposition. Again, Gödel's theorems actually prove this. This ties in with your observation on axiomatic systems, so there does seem to be a kind of parallel with natural languages because both axiomatics and natural languages are insufficient to fully capture truth. But this view only makes sense on the assumption that we are approximating some truth.

Rescher developed a coherence theory of truth that is interesting, but I haven't looked at it in ten years.