Could be interesting, but it’s worth bearing in mind the N.Pennines mtb sportive was cancelled (due to lack of interest/conditions(??)) and probably offered as good a course as this might.
If you’re doing things officially, much of the tops are footpaths AFAIK which might cause you problems. And given a mid summer date is peak for walkers doing the Pennine Way, you’d likely want to minimise using stretches of that to avoid any potential antagonism. If you don’t go to the top then will that put people off??
There are a couple of obvious routes that aren’t ROW that you might look to secure landowner permission to use to loop round in the Eden valley and Cow Gill if you are going this way – you are probably onto this though.
Given the unpredictability of ‘summer’ there are a couple of potential routes that I definitely wouldn’t be interested in ‘racing’ or riding in groups on as they’d likely get even more trashed than they have been in the last few years. Can you get good and bad weather options that are fun to ride and would help you to keep the event on in all conditions without royally buggering the tracks up if it’s like last year?
Might be worth getting on to someone at the AONB in Stanhope and see if they could help out marketing it – might be especially willing if you are going for the whole ‘helping increase accessibility for people who wouldn’t otherwise go…’.