Seriously? Universes beyond?

Quote from Lia_Black >>

I believe my only real complaint is taking content that should be in a setting neutral book, such as Swashbuckler, and putting it in a book designed for a specific setting. Otherwise it is just another campaign setting book to be bought or ignored as you see fit.

I guess not so much a complaint as an annoyance.

 That's fair, but it's also not unlikely that, if the book wasn't going to exist, we wouldn't be getting the updated subclass any time soon. The regular D&D releases have their own needs, and if Swashbuckler (or any other subclass) doesn't fit, they're not going to increase page count just to make it available. If it does belong, I suspect we'll see it in the mainline book as well.

It's also not really any different from a practical standpoint to options appearing in a FR or Ravenloft book.

And eventually, I fully expect we'll get a book consolidating the setting-gated player options, or at least the good ones, like we did in the 5e era. 

Imagine that the only way to play a Bladesinger was through SCAG?

To be fair, the Bladesinger was a subclass based on setting specific lore and the elves. It really belonged in a proper setting book. Swashbuckler doesn't have ties to any specific setting or lore.

Quote from bthec18 >>

Imagine that the only way to play a Bladesinger was through SCAG?

 That's still a D&D set book, not a different IP. So it's apples to oranges

Quote from bthec18 >>

Imagine that the only way to play a Bladesinger was through SCAG?

 In current 5.5e the "only" way to play a Bladesinger is through Heroes of Faerun.  What's your point?  The only way to play an Artificer in 5.5e is through the Eberron sourcebook.  The only way to play a Grave Domain cleric is through the Horrors Within sourcebook.

The World of Warcraft sourcebook is being produced by Wizards of the Coast.  It's just another setting book that contains subclasses usable in any world.  This is how it's always been done, except when Tasha's and Xanathar's did a roundup of classes to get them into one book and clean them up.  And I'm sure that down the road, they'll do the same thing for the current crop of 5.5e subclasses.

You're forgetting that there were seven years between 2015 and 2022, where: 

Quote from bthec18 >>

the only way to play a Bladesinger was through SCAG

 No imagination needed.