Win98 is going to make 15' monitors hot again. Win98 contains built-in support for multiple VGA cards and monitors tied together by a virtual desktop where you roll the mouse to the right and the pointer jumps across to the monitor on the right. A 21' monitor with approx. They can reuse all the 13' and 15' monitors mothballed by power users.
Upgrades can be incremental and scale well beyond existing single monitor limits.
Multiple monitors are the economical way to go now. In the future, as software developers adapt to the new paradigm they'll also be the productive way to go. Imagine accessing Word's menus and toolbars on one monitor with your document maxed out on another.