Sure, but you're either going to have to generate the whole font up-front(can be many thousand characters) or you need to re-upload as you use/generate new characters which can thrash unless you're very careful about the regions you lock(and you have a driver that behaves appropriately).
Most font renderers I know do a tiered LRU cache of 3-4 texture "pages" which hurts your drawcall batching but tends to be a nice tradeoff in texture usage.
Okay so I dug into this. There is a font cache on the GPU and another in CPU ram. I believe it will fall into the drawcall batching issue you are concerned about... but terminals don't need to get >60FPS in most cases.
Most font renderers I know do a tiered LRU cache of 3-4 texture "pages" which hurts your drawcall batching but tends to be a nice tradeoff in texture usage.