ASEAN obvious doesn't trust China, but they can't rely on US either, so best outcome is they get some deal such as joint oil/gas venture, and share the fishing ground etc with china. China obvious don't want US to get involve so they wont pushing too hard on ScS, will use carrot and stick, Philippine is a good example, china basically allow Philippine fisherman go back, promise more investment and more imports from Philippine etc. I'm sure other ASEAN see this too. In 10 to 20years, if china become more powerful in term of military and economy, then its gonna be harder to get a good deal then.
as long as china don't disrupt the shipping lane(no reason for them to do so), or been too aggressive, US can only do FON operation as non-claimant party, it already said itself been neutral in this. If China and ASEAN come up a deal, that basically exclude US from getting involved, which is exactly what China wanted. the initial code of conduct between China and ASEAN just a draft, they will hammer out the details in the up coming years.
I think ASEAN realize they can get a decent deal with China due to US-China power struggle in the region. India in a sense is doing the same, not willing to fully join US indo-pacific strategy such as Australia/Japan, but take advantage of the situation between China/US to get max gain.