One of the main reasons that BIS implemented Steamworks in ArmA 3 is to deal with issues like this, creating and maintaining such database would be very difficult and costly to make, whereas the Steam Workshop is a readily available solution that exists.(And even that is taking them a long time to implement)
So it's very unlikely that BIS will do their own addon-managing database.

playwithSix network would work well in this situation. Currently Arma games need to be restarted if you want to edit the list of addons running with the game, so a solution would need to be found to have the addons become available in-game without the restart.

The word you want is "integrate", not "inter-grade". ;-)

In any case, this is very unlikely to happen for two reasons:

1. Under the MOSCOW principle, it is under the Want category -- or "Would be Nice" category, if that makes it sound better. It would be a large amount of work for something that isn't a critical feature.

2. They are already too inured in the Steam Workshop to back out now. As a point of interest, for instance, review how much work in the recent development branch changelog (http://forums.bistudio.com/showthread.php?149636-Beta-Development-branch-changelog) was undertaken just to remove all of the GameSpy dependence on multiplayer matchmaking. As BIS have been working on introducing addon loading features into the Workshop for some time now, a similar amount of work to the GameSpy removal would have to be undertaken -- and then an entire support structure for a new add-on system would have to be begun anew. =)

In short, while it would definitely be nice (and as far as I'm concerned, the farther anyone keeps anything from Steam, the better -- I was *furious* when I found out that Arma III would be Steam exclusive), it's something that our technical realities just won't allow for. And that is a major shame, for everything that you stated above about the Steam Workshop is correct.

Marked resolved on author's request