Another point of the Specialist Game Rant the I mentioned in Part 1 is that the purpose of the "side games" was to draw in new blood with the side games, in the hopes of hooking them into playing the more expensive flagship games. What GW supposedly found was that the veteran players were being pulled away by the specialist games rather than new players being hooked into the hobby by them.
On the other hand, I know several people who are gamers but not miniatures gamers, who stay away from GW stuff simply because they don't want to invest the time and money required to buy and paint an army (this is also a primary reason I don't play MMORPGs). In such a situation, a smaller game like Battlefleet Gothic would be much more palatable to them, as spending less than $100 can get you a decent fleet that won't even take very long to paint--even though many of the miniatures are still expensive metal.
But it's a maxim of the business industry that it costs ten times more to attract a new customer than to keep a current one. Every veteran of Warhammer or Warhammer 40k is going to get burned out eventually, and want to play something else, if only for a while. If the specialist games exist, the veteran will likely go to those. Even if the veteran never comes back--they're still playing within the company. If the specialist games aren't available, then the veteran might just leave the company and play another company's game, like Warmachine. And then they might like that game better...and never come back.
I find myself in that position right now--after not playing Warhammer 40k for a while, I'm looking at Warhammer a little bit, but it'll be a long time before I can build up a workable army, so my motivation is low. In such a situation, I'd be interested in checking out some of the other games, for example Warhammer Quest, Man O'War, Mordheim, Necromunda, who knows? But none of them are readily available.
The main one that is right now, Battlefleet Gothic, is great, and in fact that's the last game I played. Many of the people who have read my battle reports have said that they've enjoyed that I've incorporated Battlefleet Gothic games into my 40k mini-campaigns. With GW support of other games, I could potentially do the same thing with them... (for example, a Mordheim or Man O’ War game incorporated with Warhammer. How can that not be cool?). GW would do well to have more cross over campaigns and battle reports. The intermingling of fans of both games can only serve to increase the popularity of both.