You two are shallow. [fused-head NP?]

Here, "you" acts as the determinative and "two" as the head.

In The Cambridge Grammar of the English Language (pp. 421-422), the following is written about "we" and "you" in the context of fused-head noun phrases:

The fused-head analysis avoids the need to recognise a large amount of overlap between the pronoun and determinative categories. In the present grammar there are just four items that belong in both categories: what, which, we, and you.

...

We regard the we/you students construction, therefore, as involving an extended, secondary use in which they [we and you] have been reanalysed as determinatives.

The we/you students construction is the same construction as the you two construction in your question. Therefore, "you" is the determinative, and "two" is the head.

Thus, if you remove "two," you are left with "you [two] are shallow," in which "you" is a fused-head noun phrase (determinative-head).

Edit:

I couldn't find any previous use of the we/you students construction that is mentioned on p. 422, so I'm not totally sure where/if they mentioned it first. Nevertheless, I did find an example of the same construction using "Irish" instead of "students."

A side-by-side comparison between "we/you" as a determinative and as a pronoun on p. 422 is:

a. [We/You Irish] will have his support.

b. [We/You] will have his support.

In sentence (a), "We/You" acts as a determinative, whereas in sentence (b), it acts as a pronoun. It is quite clear that the function of "you" in "you two" is the same as it is in "you Irish."