Where GW differs now is that they are actively looking at the game and providing regular updates with FAQs in a quick and predictable method. Gone are the days where you have to wait 6 months for a codex FAQ. Gone are the days when a broken rule remained broken because they didn't want to change a core mechanic.
Yeah, this is a great development and a marked improvement over what went before.
This idea would take that even further, and fully digitalise it. With reference to what Partninja, Blazinghand & Wyddr said, it would go something like this:
You would pick the ‘Warhammer 40,000’ App, and this would cost you...whatever a month. For that you get the core rules, and every codex and supplement. All the rules there are in the game, right there in your hand. When a new faction is created, it’s simply added in.
Then, every month you get an alert telling you that from the 3rd, unit A will now cost X points, or that it has Damage D6 now or whatever. And these changes will be added automatically, without the player having to do a damn thing.
Books can still be a thing; but now they can focus purely on fluff and modelling. No more outdated and worthless books, full of obsolete rules.
I would probably make a separate app for each game system there is; one for 40k, one for AoS etc. They should probably work out the same as buying 3-4 books a year.