Entrenchment and Diplomacy compatible with Rebellion?

What do you mean?

Most if not all of the entrenchment and diplomacy features will be in rebellion.

We dont yet know if you install rebellion with/over diplamacy or if it reqires a seprate install.

If one player is playing rebellion and another player is playing entrenchment they can't play the same game, however the player with rebellion will also be able to play entrenchment and therefor play together.

Mods will almost certainly not be compatible.

System requirements should be about the same, possibly a little more or less depending on features added and optimization's.

That's what I meant, thank you.

I don't think we know that yet.  If someone buys Rebellion and never owned any of the other games he might be limited to playing Rebellion.

I was pretty sure you got the older versions when you purchase rebellion I will look it up.

Edit: I didn't find anywhere where it said Trinity does or doesn't come with Rebellion, if it doesn't there will probably be some bundle deals you can get at or shortly after launch, or maybe even a pre-order deal where if you pre-order the game you get Trinity. (I don't see why you wouldn't get the earlier versions with rebellion)

at a min, you get all the old content... so if you have rebellion, there is not point to buying the other things if you didnt already have em.

unless you have a friend who is refusing to upgrade for some dumbass reason... in which case you should buy him rebellion, instead of downgrading yourself.

It's not exactly going to be free.  The barrier for someone who owns Diplomacy is $30, and it's $40 bucks for those who just own regular Sins or Entrenchment.  It's conceivable that some casual players might not want to drop that kind of dough on the game even though they have may friends who just bought Rebellion.

Rebellion will contain all of the current game content because - as Kitkun noted - we're building off its codebase.

For existing Sins players, Rebellion will be adding a great deal of new content to the game; for new folks, it'll be something quite remarkable (we hope). 

If newbies can't work their way up through the earlier versions, one concern might be that Rebellion will be overwhelmingly complex.

Especially with the current lackluster set of tutorials.

Seconded, Zeta1127.
I'd love to see more tutorials on things in Entrenchment and Diplomacy, especially about Starbases and Envoys. 

The intention is to redo the tutorial system for Rebellion.