First things first, a common error among 40k players comes from their ignorance of the English language.  So, many of them see "heresy" and think that it means religion.  Although religious heresy is the subject of the primary definition of the word "heresy", it is not the only one.  So, when Space Marines, including Black Templar, speak of "heresy", it does not automatically mean that they consider the Emperor to be deity.  So both the priest of the Imperial Creed (who mean the religious type) and Space Marines can speak of "heresy" and not have the same import.  Why?  The other (and possibly original) definition of heresy:

a :  dissent or deviation from a dominant theory, opinion, or practice
b :  an opinion, doctrine, or practice contrary to the truth or to generally accepted beliefs or standards

So, you can have a "scientific heresy", "political heresy", "social heresy", or even "40k list building heresy".  It does not require acceptance of the Emperor as deity.

On the subject of the recent retcon, a number of people flinched and said they could "see that" BT might venerate those who had "touched the Emperor" (sanctioned psykers).  I thought about agreeing, it kinda, sorta sounded reasonable, but something kept stopping me from doing so, even though I remember arguing that since the Emperor had sanctioned Navigators and Astropaths, the Black Templar would accept them, so it wasn't that big a deal, right?  I found the answer in some of my recreational reading.  It goes a bit, you have been warned.

So, I"m assembling a LRC for a little 5th Edition 1250 point partners game (Yes, 5th).  In between gluing bits while I retire from the fumes I've been re-reading Helsreach for the umpteenth time.  Now I'm not worried about the various nifty USRs or how badly our vows are going to get hammered or the fact that GW in 6th has painted themselves so far in the corner with 6th they only have two options with most of the middle denied them.

•  Turn us into some variation of vanilla Marines while they use pages of Helsreach to wipe their arses because its been retconned into worthlessness.
• Actually cut us loose to actually match our fluff from both the older codices and Helsreach, which will cause massive shrieks as we get reviled as the "Cheese" Templars.

I'm expecting the former, with AACNMTO continuing to be Rage, which is the equivalent of SW Blood Claw "Headstrong".  Righteous Zeal remaining some variant of the current Righteous Mild Enthusiasm (IMO, they should at least go back to the original where we are forced to move, but it only triggers on a failed morale check and then we "fallback" towards the nearest enemy.  However, those are special rules, what I want to think about are the actual squads...

Including Allies can be a lot of fun.  How do we justify it in some cases?  Well, speaking as a Black Templar, I find a few oddities in our choices of allies, but the trick is to make it "fluffy" for fun.  For other Space Marine chapters, it is simply joining together for a similar purpose, but IG can be a bit more problematic, although assuming that the Crusade arrived at the target location to be joined by or to join with other Imperial forces fighting in the same area.  Here is one way to do it though...

Rumor this, rumor that, there have been so many rumors around and around that between people claiming to have a "mainline" into GW being cagey, to people who can fake GW well enough to make things up, it is all contradictory.  Rumors of making vehicles weaker, rumors of making vehicles tougher, rumors about new movement rules, shooting rules and assault rules.  With all that, I'll make a prediction you can take to the bank...

GW is totally ignoring the 8000lb gorilla in the room.  After all, this isn't a mere "rules update" or "adjustment", this is supposed to be a whole new edition!  If serious changes need to be made, now is the time to make them!

This is a fluff commentary. 

One question that seems to come up among people new to the 40k universe is "what happened to the technology?"  Especially when there is actually so much there, what we have left are hand crafted artisan work as the height of technological mastery other than what is covered by a STC.  My theory is that genius comes rarely to the human race and the "spark" that makes for the technologically innovative mind is related to the "spark" that makes a psyker.  Not that it is new, but I've seen it a lot in fiction.  Steampunk makes the connection close (as well as the Gothic connection) and I think that is simply what has happened in the 40K universe.  At the time of the Emperor's being placed on the Golden Throne, the only Imperium approved psykers were those related to the Navigators and astropaths(?) and possibly those who used "faith" powers that may or may not draw on the warp.  Not being stupid, either prior to or in the aftermath of the Heresy, it was noted that there was a relationship between general "modern" and "technological" learning and warp taint.