I didn't bother to read this extensive and branching debate, as I didn't feel it was necessary.
The Nature of 40K
There are a few things you as a player should understand when it comes to the structure of 40k. The first and foremost is the Purpose of the rules. The rules are permissive, telling you what you can do, and when necessary for clarification, telling you what you cannot do. This is because the rules are also trying to be the impartial, neutral judge/official, keeping the game fair. Unfortunately, the only way the rules gain any power is when the players all agree to use them, and there is no way to realistically penalize someone for breaking them within the game.
Second, for better or worse, the rules are written by Brittish employees to Games Workshop. After 15-some years of 40k rules debates, I've learned that for the Brittish, RAI = RAW. That's why there's a bunch of fluff interjected into the rules themselves. Unfortunately, I'm American, a society founded by a bunch of people who argued violently about semantics in a few books. We have more lawyers per capita by a huge margin, because for us, RAI /= RAW. Period. While that ultimately leads to rock-solid rulebooks for our games, it also leads to really long and boring rulebooks. The NCAA rulebook for Football is 264 pages of dry, clear-cut, concisely worded rules and diagrams. Or, read the Adepticon FAQ, which tries to turn the 40k Rulebook into an ironclad rulebook: The Independent National Warhammer 40,000 Tournament FAQ V 4.0.
If you turn to page 87, you can see how they rule on the Shrike Issue, along with Rulebook citations. They flat-out state the RAW do not allow Shrike to Infiltrate a unit, but this FAQ creates a Rule Change to allow Shrike to Infiltrate any unit as long as he is deployed within coherency distance of this unit.
The INAT FAQ is a great document, as it serves as an impartial judge/official for a 40k game, and it covers everything. I may not agree with some of their rulings/interpretations, but it leaves little room for arguement if both players agree to use it.