What about Global Express or a GV?
At the risk of being too controversial why does the R1 replacement have to be a large aircraft at all? Given that the RAF happily operates Predators, soon even for combat missions, from half way round the world relying on data links, why not put the sensors and processors and a limited number of mission "managers" to monitor and "optimise" the mission and provide an element of airborne "redundancy" on an aircraft such as Global Express (commonality with ASTOR and faster, higher and further than the R1) or GV and send the data back to be analysed on the ground in real time? Also less aircrew at risk. I know, because I was part of the Team, that a US systems company made such a proposal to MOD at least 10 years ago, and had carried out a wide ranging study of the concepts. Sensors and particularly computers and data links have got a lot smaller since then. Needless to say such a radical proposal was not well received by MOD!
JB