So… No different to having alts, except you dish 1k gold upfront.
You’re overthinking this big time. You need to remember that DS or not, you’d still have to get the gear to replace another player’s main, otherwise any raid leader would simply go with the main. The stunning majority of guilds will not give gear to alts or for offspec easily, because mains have priority (at least until they have the content on farm and mains don’t need gear anymore). This is the primary reason why I don’t think having DS would be expected, and I’ve certainly not heard stories from Retail about it ever being expected.
Normally DS would be used exactly like alts are used now: farm something, cover for someone who can’t come/needs to drop out, run alt raids, PvP. So for regular guilds that don’t go for world firsts, DS would most certainly never be a requirement.
Sure, but you still can only use one at a time. Otherwise you simply go for a hybrid spec, don’t unlock DS, and save yourself a grand.
But the social interactions aren’t going anywhere. Really, DS is not very different to having an alt.
That’s not going anywhere either. Even right now, without DS, you could still have someone log an alt as another possibility. I covered our guild AQ40 on my tank when one of our regular tanks was undergoing surgery. With DS ingame, it still could have been me covering, or one of our fury warrs who have tank gear switching to tank, and us inviting a dps. I don’t see anything weird about this.
I get the impression that you consider DS to be some alien, malicious concept that would destroy the game, and it just isn’t that. In principle, it really isn’t all that different to having alts, it just lets people do other things on their main rather than an alt.
Well, I didn’t.