Excellent questions Biggus.
The political pressure (both internal MoD and from Government) will be immense. We know this pressure often prevails over common sense and regulations. Chinook HC Mk2 for example. Nimrod was scrapped because it could never be certified and it would be slightly embarrassing for a replacement for a Nimrod variant to go the same way. The fact MoD have admitted "challenges" merely illustrates their utter failure to learn lessons over the last 20-odd years. The ludicrous Wg Cdr Spry thread here on pprune encapsulates the problem. The Flight Safety organisation can't get basic definitions right, even when MoD regulations get them spot on.
-re historical evidence. The rules governing technical and financial approval require this issue to be squared away under, at worst, a risk reduction programme, long before any development or production contract is let. Lack of such evidence has been regarded as a standing risk on all aircraft and equipment programmes since the Chief Engineer created the risk in 1991 (by issuing directives that savings should be made at the expense of safety). All aircraft PTs know it must be mitigated up front. I'd bet my house this has been largely ignored, in part because it is a career killer to implement this legal obligation and discover a problem. Nimrod MRA4 again.
Additionally, and as stated before, one cannot simply buy an aircraft, especially the avionics suite, "off the shelf" from the US. Our Home Office dictate certain parts of the specification which the US don't even know about (and they don't tell us of their equivalent). If the project has been planned assuming the aircraft will just be delivered and flown immediately, then some rather significant parts of the build standard and clearance process have been ignored entirely. Again, mandated risk reduction stuff on Day 1.
Another problem, as discussed above, is a distinct lack of corporate knowledge, not unrelated to the horrendous uncertainty anyone working in DE&S faces at the moment.
I think it will enter service, but the operational constraints and limitations may mean in some respects it is a dumbed down version of the R. Or perhaps the long delay means MoD are beavering away getting it up to spec.