The form of the verb is determined here more by meaning than grammar. The
only way we can understand the sentence is by understanding the ellipsis.
In your sentence “I will be home before you (will)”, the action of the
verb is the same (“being home” in the future). The difference is only
between the agents (or subjects) – I and you. With the ellipsis, we
understand that the missing words are " … before you will be /
are home.
In the sentence “I will be done before you arrive” there is no ellipsis.
There are two different actions: “I will be done” and “you will
arrive”. So there is no ellipsis of words or verb form to understand, and the
form of the verb will be determined by the use of tense after “before”.
Note that as I said in my earlier post, the versions with “will” (2 and
5) are unnecessarily longer, (but not unacceptable) and when we speak in
everyday style, we normally choose the shortest and simplest way to convey our
idea, unless there is some other stylistic reason (rhetoric, emphasis) to choose
a different form of words.
English grammar is often descriptive (it tries to explain
how we use grammar) rather than prescriptive
(it sets rules about how we must use grammar). Your source is
an American crime drama, and we don't know about the background of the speaker
and the precise context. These always affect people's style – whether
they're speaking carefully or carelessly.