The Allies matrix makes very little sense.
Eldar and Dark Eldar being brothers in arms is actually fine. They may have powerful philosophical differences between their cultures, but they both know damned well what will happen if they let those differences get in the way of survival, so I see no reason why they cannot work well with one another.
Also, tourney legal Corsair lists perhaps?
As mentioned, Space Marines now like and trust Tau (and vice versa),
Don't like this one. Like what it implies about a possible fluff shift even less. Space Marines have been the galaxy's intolerant, xenophobic jerks for twenty five years. Why is this changing?
Imperial Guard will totally fight alongside Chaos Daemons...
Remember, Guard represent a ton
of different things. All the way from some middle tier PDF to crazed heretic traitor Guard.
My personal favourite, Sisters/Black Templar are an Unholy Alliance, despite, y'know, agreeing about almost everything. Abhor the Witch, Burn the Mutant, Kill the Heretic and aparantly, Hate Each Other!
This is one of those matches that seems
like it would be automatic. However the Templars and Sisters believe very
different things. Sisters believe in the divinity of the God Emperor. The Black Templars, on the other hand, specifically deny that lie, and are practicing the worship of the Emperor himself, and are stuck 10,000 years in the past carrying on with the Great Crusade/Scouring.
Have to be sure to not get confused by the fact that they are both religious themed and hate psykers. Their beliefs are similar, but it's actually a very common real world occurrence for two very closely related offshoots to be totally irreconcilable. The best comparison is actually Space Shiites vs Space Sunnis. Cirrusly. Go look up the difference between Sunni and Shiite Muslim beliefs. It's crazy what these guys have been carrying on a bloody civil war in Iraq over for decades
. In the end, that's the kind of minor difference in interpretation that might make the Templars and Sisters not likely to get along too well. I mean, they're not likely to be violently antagonistic, but they definitely shouldn't be good friends.
The other part is that the Sisters are extreme rules lawyers. It's what makes them such good enforcers for the Ecclessiarchy and occasional tools for the Inquisition when hunting supposed heretics. The Black Templars, on the other hand, are running a heretically illegal amount of ships, Marines, and weaponry. So, in addition to being Space Marines (who inherently don't consider themselves subject to the authority of other Imperial agencies), they also wouldn't want Sisters around, tracking their movements, and snooping into the secrets of the Crusade Fleets, lol.
I like to put it this way. It's the difference between the following conversations:
"You hate witches? We hate witches. There's a witch over there. Let's go burn her."
"You hate witches? We totally hate witches. We should hang out all the time and burn witches. But you have to promise not to tell anybody about our illegal army, illegal fleet, or our questionable recruiting and training practices. Oh, and realize that we're probably never going to treat you as equals, and we think your whole religion is total bullcrap. Oh, and it's cool if you report back to your buddies at the Ecclessiarchy, the Inquistion, and the High Lords about where we are at, and where we are going."
Honestly, the Sisters of Battle probably have too many
Allies of Convenience, lol. They should be Battle Brothers with the Guard, AoC with Grey Knights, and Desperate Allies or "No Allies" with pretty much everybody else. They aren't exactly known for playing well with others.