focusing on the ground glass with ultra wide angle lens (larger than 45mm) and digital back isn't really easy... but using the ground glass for composition is way better than a range finder !
So Sinar Artech and Arca RM3D+ rotaslide are for me the two valuable system for architecture... ground glass and perfect focusing... and tilt !
If same type of screen and live view as the 5DII was possible with a digital back, it will be an other story !
and even if mf backs would offer such good live view and lcd as the 5d2, i`d probably still prefer to compose the image on the groundglass. its somehow a more physical contact with the motif, far less abstract than the lcd live view transmits.
next generation of photographers whi will grow up with digital probably might feel this different. i am educated by 4x5" work and groundglass composing, so this comes most close to what i am used to do.
focussing for architecture is normally not a problem cause many motifs play at infinity. even in interior shootings with wideangle use focussing isnt that critical. and to control the 100% view in any case is the way to go. images can be blurred by several reasons, it has not only to be an unaccurate focus setting, so better to check each shot afterwards a second.