For how long is that Newcastle period going to hang over Shearer if he genuinely was interested in getting back into the management circus once again, be at club level or international level??
At least he was brave enough to accept that role, it is not an easy task being a manager at any time, and that period I think can only have benefitted him in terms of it being a learning experience, that he can use in the future.
If he really did want to be the next England head coach, then when looking at the other possibilities, in terms of English options, then I would not be so quick to rule him out.
Presumably, since that time at Newcastle, he has got all of the available badges (I don't know if he has or not), if so, then I don't see any major cause for concern if he were to be appointed, any more so than anyone else, as until the actual system is updated, whomever is in charge will continue to be a tad hamstrung anyway.
Better for that person to be English, then someone not in that case I think.