What is wrong with a question about coordination? Isn't that question relevant?
The title of your question is 'Adding Emphasis', but you then ask about 'coordination' when in fact your question appears to be about verb agreement.
What exactly is it that you want to know?
Maybe it's not the right heading but the issue arises when a pattern adding emphasis is followed. My question is whether the verb is coordinated with "parks", which is plural, or with the following word - "what"? And does it (coordination) go in a certain direction or is there another consideration when choosing a singular or a plural verb?
The beautiful parks are / is what I like about London.
This is about 'number agreement'.
Verbs normally agree in number with the subject, and since "parks" is plural it follows that the verb should be the plural "are".
Override can occur with some collective nouns, number-transparent nouns like "lot", and certain measure expressions:
(1) The committee has/have reached a decision.
(2) A lot of errors were made.
(3) Eggs and bacon is my favourite breakfast.
In (1) the collective noun "committee" can be conceptualised as a single entity or a collection of members, and can thus take singular or plural agreement.
In (2) the head of the NP "A lot of errors" is the singular noun "lot", but the verb agrees with the complement of the preposition "of" (which here is the plural "errors") -- and thus plural "were" is required.
And in (3) "eggs and bacon", though a plural noun phrase, is seen as a single unit, and hence the singular verb "is" is required.
This is a really exhaustive answer, I'm grateful. Actually I was thinking whether "London's beautiful parks" could be seen as a unit, I know this rule, but obviously I was wrong.
London's beautiful parks are worth a visit.
The noun phrase "London's beautiful parks" has the plural noun "parks" as head, so the plural verb "are" is required.
Yes, it's absolutely clear this way.