But not the way I want it. Basically, in 7DS for example, we have 10 races. Some of those races I want to be Xenophobic from the very start of the game, and hate every other race, except themselves. If they run into a player of the same race, they would befriend them, but will want to war with all the rest. I also want some races to love everyone, and be loved by everyone. That kind of thing, which harkens back to the old Master of Orion days, where picking certain races would mean you would be hated by other races automatically.
I am still not following why this could not be done already. You can set a specific bonus or penalty a faction gets to every other faction in the race.entity file. A Xenophobic race could have large negative modifiers for every other faction. This is basically what the TEC Rebels already have. Others like the Vasari Rebels could be made more cooperative towards everyone (you do seem to be in a bit of a logical bind of what happens when a xenophobic race meets a popular one, but I don't see what could help you in that situation).
In addition, for races that are supposed to have very good Diplomacy, you could give them the relation research modifiers at the start of the game.
I currently have 9 factions and they all have customized starting diplomatic values towards each other, based on the lore of how likely they would be to ally.
You could theoretically, but you would have to sacrifice the ability to destroy planets... if you made the stripped to the core definitions in reverse, you could for example do something like: Asteroid -> Barren World -> Desert world -> Terran World
But stripped to the core would become terraforming. So you would no longer be able to reduce a planet to resources =P
This exactly. Mods may choose to allow destroying planets, or terminating them. It is unfortunate you cannot have both, but that is infinitely better than what we have know, and it seems rude to complain over getting an ability to be able to do this when we couldn't reliably do either before. 
We might even be able to teach the AI to destroy and terraform planets now, which was totally impossible before.
I believe, though I'm not 100% certain, that you could make those resource numbers negative to make it cost to 'strip'/terraform... though I haven't actually tried it myself.
Once we get the ability to change planets, by far the most sensible thing would be to make the Terraform ability itself cost resources. That way, you could not actually attempt to terraform until you have the money. Even if negative resources did work, you could still try to do it if you are broke. 
