Already available?
A quick trawl of the prominent online tat-emporiums reveals MTK6582 Mali-400 based phones can already be had for a fair bit less. One with a similar spec to these three; Generic English language Android KitKat, 4.5" 480x854 IPS but an 8MPixel rear camera is currently advertised at £49 delivered.
If one is prepared to drop down to the PowerVR based, but still quad core MTK6589, then £35 secures a 4" 480x800 but otherwise similar model.
Is the extra cash worth a few software updates from Google?
I would be immensely happy to see Canonical specifically targeting their OS at these ultra low-cost phones.