The number of distinct glyphs available in Mists of Pandaria is increasing from 345 by 56 to 401 (correct me if I'm wrong, or this changes). Most glyphers that are strong in the market have organised their operational efficiencies based on the space that glyphs take up in their inventory.
For example, @Stede wrote a guide to selling glyphs on a single character, opting to not sell low performing glyphs to save on inventory space. I used the concepts in that post to streamline my operation to two characters, because I'm a full service glyph machine. Other glyphers have as many posting alts as it takes to store an operational supply of glyphs in bags, so they don't have to run to a bank during their posting cycle.
However you sell glyphs, some consideration needs to be given to how that should change for Mists.
How I will change my two character operation
Twitchie uses 7x [Royal Scribe's Satchel] in his bank to store up to a stack of each glyph for regular posting cycles.
36 slot bags x 7 bag slots = 252 distinct glyphs.
My glyph posting alt uses three bag slots for glyph storage for 108 distinct glyphs, bringing the total to 360, comfortably accommodating all the glyphs for Cataclysm.
So for Mists, I'm going to tell my glyph posting alt that they are going to absolutely have no life and grab another stachel for her bags. I guess while we're at it we can use up some of her backpack as well.
252 slots in the bank
144 slots in inscription bags
5 backpack slots
Total: 401 slots
It's reasonably minimal disturbance to avoid expanding the operation to another character.
The challenges of a single character operation
The major downside of a single character operation is that we just don't know what will sell and what won't in MoP. We can assume that many current trainer glyphs will still perform poorly, but given the predicted surge in demand, a single character glypher risks losing out on a share of the profits for the next glyphmas.
Scale up for Glyphmas
I'm going to assume that anyone who has successfully scaled back their operation to a single character has analysed glyph performance and has gone through a similar process to Stede's post. So for those people, scaling up for the new expansion should be relatively straightforward, and if they have an alt they can spare, expanding to my two character operation could be just the ticket. Alternatively, you can clean out the bags of your least favourite alts and load them up with glyph stocks to post for patch 5.0, MoP and beyond.
Scale back after the dust has settled
Looking ahead to a couple of months into the new expansion, new herb prices will have fallen and will be more stable and the glyphing community will have burned through much of their stockpile. At that point, a single character glyph operation can resume, using a couple of months worth of glyph performance data.
The impact on a multi-posting operation
For a true, "look-ma-I-have-a-seccond-account-just-for-posting-auctions-cross-faction-arbitrage-and-characters-galore" operation, I'm going to assume that all slots can be used on each character, including the backpack.
16 slot backpack + 4x [Royal Scribe's Satchel] = 160 bag slots.
160 slots per character, and 3 characters later you're up to 480 glyph slots already. So, as you were... you can just divvy up the new glyphs into your TSM auctioning groups, auto mail them and continue on enjoying the glyph market as you did before.
How will you modify your glyph operation to accomodate the extra glyphs in MoP?