As it exists today
The most obvious choice to substitute “as it exists today” is contemporary (sense 2) or present-day, but those are not very elegant as adverbs. I would probably rephrase it a bit:
This document surveys the ethnic making of Manhattan, both historical and contemporary.
This document surveys the ethnic making of (both) historical and contemporary Manhattan.
This document surveys the ethnic making of (both) historical and present-day Manhattan.
— or just do what @ErikKowal suggests and use today, which is perfectly valid, even if it is less prolix.
After upcoming expansions
Obviously, contemporary or present-day will not work to describe a situation that has not yet arisen but is expected to after upcoming expansions.
This situation is really just describing a future situation, but it is also quite specific in that it mentions a specific set of expansions to be carried out. There is no way of simplifying that to a single word or expression—just use what you already have.
If you are looking for something to describe all three points in time (historical, now, and in the future) and don’t care too much about the details of the expansions, you could say:
An analysis of the subway system capacity, (both) past, present, and future.
(Note that some people consider both in such a sentence to be ungrammatical, claiming that both must be followed by exactly two options, not three. If you are writing a formal text, it is probably best to leave it out; but to me at least, leaving it in yields a much more natural sentence.)