Concord with gender-neutral "they" [duplicate]

I was wondering what the general take is on concord with they as a gender-neutral 3rd person singular pronoun. I assume there are no hard and fast rules here yet, seeing that this is a fairly new phenomenon – or am I mistaken here? If there is, indeed, an established rule, please let me know! But if there isn't, what is your view? Do you think grammatical meaning should determine concord (example [1]), or do you think semantic meaning should determine (example [2])?

[1] If someone wants this, they have to let us know

[2] If someone wants this, they has to let us know

I can't help it – [2] makes me cringe... even though I realise that there are equally good arguments for either.

What's your view? :)

Solution 1:

I might be wrong, but I've never heard "they has" in that context. Singular they is not a new phenomenon: see Wikipedia and Merriam Webster (which has quotes from William Shakespeare and Jane Austen). All the examples I can find with singular they have a plural verb: they have, they are, they do.