Are there any EEG procedures currently available/in development that can formulate letters/words from deliberate, internal monologue?
What you are looking for is Imagined / Silent Speech Classification (my best guess). I'm interested in this for a few years (exactly to work with Vim) now and  worked with some of the cheap EEG headsets like Emotiv EPOC and Neurosky MindWave Mobile. 

A paper on it:
http://www.scipublish.com/journals/ABSE/papers/1021

Patent applications:
http://www.freepatentsonline.com/
To the above link, add these at the end:
WO2014066855A1.html
WO2014130571A1.html

(Due to a lack of reputation, I cannot post more than 2 links.)

The commercial and inexpensive headsets are good enough to detect what their APIs support:
Neurosky: Attention, Meditation and Eye blink.
EPOC: Please refer to their Cognitive Suit documentation. You can get 1-2 sets of detections done quickly. Good luck with detecting 4 states.

Search around for Silent Speech Classification. You should be able to find more details. There was a Japanese demo somewhere that uses classification on EEG or EMG to speak. I will post it if I can find it.