After looking into this for a week and then some, here's the best case I can make using rules. We know that BS Attack is a bit special since it has LOF as a prerequirement. You literally can't fail to declare BS Attack because of not having LOF since that would prevent declaration altogether. LOF gets locked in with the firing position, you'll know if you have LOF from the point you're firing from otherwise you couldn't declare BS Attack. If you could place the template first, before declaring firing position, you could violate BS Attack requirements. How? You can place teardrop templates around corners etc in a way that the main target gets hit by the template despite the trooper not having LOF. RAW it's impossible to find that spot because you can't ever declare a BS Attack without LOF. Placing the template first and then trying to pick the firing position that fits the ideal template placement can't be legal as a result. Establishing that there is LOF and making the declaration possible has to come first. So there has to be a fixed Order in which the firing position has to be established before the template gets placed (it still all happens during declaration though).
Actually it doesn't require LOF as a pre-requisite for declaration, you check the LOF Requirements "When declaring". So, why can't you declare BS Attack, and as part of that declaration: A. Pick the main target(s B. Specify weapon C. Assign burst D. Place the Template(s) E. Declare where you fire from F. Check LOF Requirements are met Or really almost any combination of A-F. The only order we know is specified is that A and B need to come before D (DTW rules implicitly require you to be using a DTW and require you to identify a main target prior to placing the template) and that A needs to come before F (because the LOF requirement of BS Attack requires a target). I'm increasingly agreeing that placing the template "as the final step in declaring a BS Attack" would be clearer, but again I can't find enough in the rules to say definitely "Sorry, you can't do that" to someone who does it differently from that while playing me.
Honestly, I think you're making up a large number of steps here, when you're essentially just specifying the details for the skill. The details of the skill have to be specified, and there are deadlines in the process for when some of those details have to be specified by. And I think you're gravely mistaken about "Declare where you fire from" and "Check LOF Requirements are met" being last. - In order to do anything with the BS Attack, you have to specify the weapon and its firing mode, that determines whether you have templates and your B value. - In order to specify any targets, or place templates, or determine that LoF exists, you have have a firing position. And the firing position for all B has to be the same. - The rules don't appear to distinguish between assign B values and choosing targets. It's simply not meaningful to try to talk about a B1 non-template attack with two targets, for example. - In order to place templates, you have to have assigned burst values. - The rules specify that the target's position is chosen at the last possible moment (before checking the distance), it doesn't provide for a delay in choosing the attacker's position. Note: The way they will divide the Burst (B) of the Weapon, Equipment, or Special Skill between one or more targets. In this situation, all the Attacks must be declared from the same point. It's a whole bunch of partial orderings, which generally doesn't matter because what the players are concerned about during a game is the end result, and 'All details and choices related to the execution of a Short Skill, Short Movement Skill, Entire Order Skill or ARO must be specified when it is declared' doesn't leave much room for "I want to do this process incrementally" for the parts where the rules don't say to wait. Disclaimer: The rules don't address gibberish statements like "For my first skill I declare BS Attack against you (pointing to the other player) not any of your models."
FWIW: I think that's mostly what he's saying; that there are certain things that need to be done (the list), but not much is said about the order in which they need to be done. He even says as much with "The only order we know... is that A and B need to come before D...[and] F."