It appears that Vocalekt Visions’s neutrinoP had been working with INTERNET on making a demo song for GUMI English. He worked with the beta sound bank, and a short snippet of a demo song titled You Are The Reason has now been posted to niconico (and to YouTube as well). The song lyrics were written as a collaboration between neutrinoP and Wolf. GUMI English has a tentative release month of February 2013 and was announced during the VOCALOID Trans-Pacific Project presentation at DC Expo this year.
UPDATE: Another English demo song has been uploaded on YouTube.