I can see potential for at least 3 pre-campaigns as follows:
Campaign 1 - The Reed Foundation

We get an insight in to what turned Dr. Reed in to a cybernetic lunatic (eg. story could be based around Rman Virgil's stories).
Campaign 2 - NASDA

We're the person responsible shutting down NASDA systems to prevent spread of NEXUS during Collapse, but with the LasSats offline the base is nuked and we get killed in the process.
Campaign 3 - The Project

See: [Cam 0] 'Scavenger Wars' Ideas Thread.
The timeline of this campaign is basically from nuclear winter to the Project HQ being set-up as per the game's intro video.
The child of the person killed in Cam 2 helps John Hammond set up The Project?
Then the original 3 campaigns take place...
Campaign 4 - A New Paradigm

What is currently cam1 - Alpha.
Campaign 5 - The Collective

What is currently cam2 - Beta.
Campaign 6 - NEXUS

What is currently cam3 - Gamma.
7. (no name yet)

This is Goth's as yet un-named campaign.
8 & 9
From what I have heard there are already discussions about two further campaigns after that.

