Already, Samsung and Acer are selling 24-inch monitors with TN panels. With LG-Philips and AU Optronics having also announced 24-inch TN panels, there will soon be a wave of 24-inch TN monitors with lower price. I would guess before the end of the year.
As the surface area of a 24-inch monitor is about 20% more than a 22-inch one, there is no reason to justify a wider selling price margin between these 2 sizes. And I am not even considering that electronic components cost the same regardless of size.
It is to be expected that the mainstream 24-inch size with split in two, with TN panels being used in less-expensive models that will eventually displace the 22-inch size as the new size/price sweetspot. Then there will be a higher price class for *VA panels 8-bit monitors with better color and viewing angles.
Finally, S-IPS will continue to be sold in a few high-priced semi-pro models.