Currently many glyphs are obtained only from the random random books. Many of these are one of the three best, for one spec or another. Here's a full list.
We'll still need these glyphs in Cataclysm. Some will be better, some worse. I doubt Blizzard will expect us to go back to farm mobs for world drops. We could get better glyphs, but unless they are plain one-for-one upgrades, better isn't going to absolute.
We can look to other professions for what may happen.
Blacksmithing, tailoring, and leatherworking patterns remained as they were; a mix of quest rewards, rep grinds, specific mob drops, and a very few world drops. They made gear which can obviously be easily be made obsolete.
Enchanting mostly followed this pattern, adding a new tier of enchants which were significantly better than the old world ones. Some were not upgraded though, but instead had new formulas added which could be obtained in Outland and used BC mats.
There is a peculiar feature of glyphs: they run across many levels of skill and therefore use a wide range of materials. This makes it likely that we won't see upgraded glyph techniques which use Cataclysm mats. We will see new glyphs, but not rehashed old ones. It's 'normal' in the context of glyph-making to use older mats. Part of this is offset by the ink trader, so in effect all glyphs can be made using ink of the sea. While glyphs use old mats for leveling purposes, they are all able to be made within the context of Northrend.
We're going to see the same pattern in Cataclysm with materials. For the glyph books, Blizzard will put them on trainers.
I used the "this will happen" tone throughout this. I have no leaks or evidence for any of this, so this is all just prediction: "this is likely to happen." Rather than constantly throwing in "might" and "probably" and "I'm guessing", I went with straightforward claims. I might be wrong, but I'm probably not, at least not in general terms.
Cat Context 101: Pokemon Go, WoW Legion Pre-Patch
12 hours ago