Want facebook, etc, on a new Huawei 'phone ?
Many will, that is why they buy their 'phones.
A facebook/whatever app is just something that talks to facebook using a their protocols. It would not be hard for Huawei to write some apps that use the protocols, I doubt that facebook would make them hard to reverse engineer - if they don't publish them; after all: better to have someone on facebook using an unofficial API than not have the user at all.
If some find the Huawei written facebook app is not good enough for them then they could always install the official one.
Will the gov't of the USA stop anyone using a Huawei 'phone from connecting to servers owned by USA companies ? I don't think so, but with Trump in charge I don't know.