Sentence structure for “all I need for now is you”?

All (that) I need for now is you.
主詞all＋形容詞子句＋be動詞＋主詞補語you
that是「關係代名詞」，帶出「形容詞子句」，當作主詞的「修飾語」，因為that是子句裡的「受詞」，可省略。
這不是「倒裝句」。

All that I need for now is you.尾重原則，通常重要的資訊放句尾。句尾是句焦點，「你」是全句的重點。「倒裝句」是一種強調的結構。但這句不是倒裝句。
You are all that I need for now.「現在」是全句的焦點。這句也不是倒裝句。

adj or noun as complement, "to be" may be omitted predicatively:-
You seemed ----S+seem
(to be) + adj/n+complement------to be all I need for now.

Language is about expression of meaning or feeling...

So if "You" is the important in a expression, either the sentence try to start with YOU or it ends with YOU will give the listener more attention.

This is how this sentence (actually should be verbal/spoken) structure is about.

IF written/spoken in a normal/formal structure:
Start from the simple sentence:
I want "something" for Christmas
I want "YOU" for Christmas
But this sentence will sound like "YOU" is thing.
So next revision - how to make "You" more important:
I want for Christmas is YOU.
This is ok but I really want YOU to know how important this sentence means to me for you:
All I want for Christmas is YOU.

All I need for now is YOU.
similar expression of the importance of YOU in the time "now".

You asked for a grammar lesson, but all you need to know is how language expressed the meaning.