Potential grammaticalization of epistemic phrases

This paper deals with the potential grammaticalization of English (it) could be and (it) might be into epistemic sentence adverbs in analogy to maybe. They can occur in adverb-like positions and functions in informal language use, e.g. (it) could be something good has begun, often with the pronoun it omitted. But, given that no diachronic development is attested, to what extent does their usage indicate innovation or an emerging convention of adverbial could be / might be? How are they differentiated from maybe? Following up on previous corpus-based and experimental research, I present findings from two small experiments. Experiment 1 elicits the morphosyntactic interpretation (clausal vs. adverbial) with ratings of structurally different paraphrases; Experiment 2 aims at the semantic interpretation of epistemic stance. The results provide little evidence of conventionalization of adverbial could be / might be, and also no clear signs of semantic or pragmatic differentiation. I conclude that weak conventions leave room for variability, and propose that these forms have a proclivity to be continuously re-innovated as micro-steps on a grammaticalization path, but this is not enough to drive change beyond existing conventions.