I'm not fond of being able to build more than one titan either. I think they would lose their impact. You should also keep in mind that if you can build multiple titans so can the enemy, meaning the two fronts might just turn into three (or both players just keep exchanging worlds by wiping them with double titans)

You don't need your titan to fend off an enemy titan anyhow, with the right defense you can still go and use it elsewhere to attack.

The Rebels are not stronger than the Loyalists (at least from my experience), but the Loyalist AI doesn't use it's specific researches as well as the Rebels (well the rebels don't use them in a smart way either, but at least the rebels can use their free ships while the Loyalist don't build their second starbase at all). The general AI behaviour has been worked on as well, as far as I know. From playing against them I would say they use smarter fleet compositions and focus more on capships than they used to.

Blurred textures? Did you set the planet/structure/ship details to highest as well? Cause my textures look pretty damn sharp on highest detail...

I wouldn't like being able to build allied capships as your own using alliances. There is a point in why each faction has it's own ships (I'm not uch a fan of unholy alliance factions). It'd be great if you could request an allied player to build certain buildings in your gravity well through diplomatic options, though. You know, phase stabilizers for example.

Maybe each planet could unlock a certain limited amount of reserved tactical slots that can be used by allies only (around 6 to 8 so you cannot build foundries or superweapons there).

I don't know...I think it'd be pretty awesome if you could tell an allied AI to build a starbase in on of your gravity wells. Or convince a Vasari ally to put a phase stabilizer or two in your territory.

On point 1:  You couldn't use the two titans on two fronts.  If you split them up, then they will just hit you with both of theirs.  yours would surely die, and then your other one is also dead, for you cannot stand against two titans with one.  I suspect that two lower lever titans could easily defeat one higher lever titan.  Titans need to stay solo. 

However, I do agree with calwyn on that it would be cool to tell your allies to build starbases at your planets.

The scaling on levels makes it that if I compared a level 4 to a level 1 titan there is none. If you have an ankylon with 5 levels against 2 level 1 rebel titans then the ankylon is gonna win especially if you are on the defensive.