- "since you can't swap glyphs in combat."

It's entirely possible that there are one or several mistakes going on here on the Dev's part. During the Ulduar PTR, Fragments of Valanyr were Unique (30) yet required 40 to complete the quest. During the Cataclysm Beta there was a bug that put all Trolls on the Human male skeleton. Sometimes wierd crap happens because wires get crossed and other times a developer in one department or another just makes a bonehead move.

Explanations:

1) Someone had a derp moment and forgot that you can't swap glyphs in combat while they were playing around with this glyph.
2) Someone was playing around internally with an alternative version of the glyph that did way more than intended, had a derp moment and accidentally put it on the Beta servers.

The answer isn't to get all pissy and bitchy like they do over at MMO-Champion (and a surprising amount here - Honestly, I really thought this community was better than that), but to say "Hey, if you want this to be an emergency thing, then it can't be a glyph since you can't swap glyphs in combat, otherwise no one will use it since no normal Warlock will give up a major DPS CD on the off chance that he'll need to tank for 5-10 seconds".