I don't think anyone knows for sure at this point.
What I read (and I can't find the post now to point to it) was that glyphs would effectively become like bags. You, as a character, would have glyph slots that you could fill...just like now.
Once you buy a glyph, you keep it and can swap it out for other glyphs that you buy. Swapping out a glyph would not destroy it. You'd bank/bag it somewhere until you needed it again.
No one ever said, that I know of, that you could buy all your class glyphs and use them like spells.
Now, that said, that's not a bit like it is now and many might find that sort of market alarming.
On the other hand, no one that I know of with tailoring is complaining about the bag market. My tailoring alt sells them pretty much at will.
So we'll just have to wait and see. All of the above was from really early on in the info dumps from Blizz.
EDIT: To clarify, I meant they would be a lot like bags as a market. You can swap bags out now all you want but why would you want to if it's not an upgrade. There are real reasons to swap one glyph for another even now.
SECOND EDIT: Just saw this this morning from the latest build...
* All glyphs are now found in the spellbook of each class on beta servers. Ultimately, classes will learn glyphs as "spells" and will only have to buy the glyph once to definitely learn it and swap it at any time.
Note the line about swapping which implies that the number of glyphs active will be limited (since there will apparently be a need to swap them).
Edited, Aug 14th 2010 7:51pm by Moanique
Edited, Aug 15th 2010 1:59pm by Moanique