I think (and I'd hope most fans would agree) that there's an unspoken code of conduct regarding joining direct historical rivals, particularly once you have reached a certain stature within club 'A', as Poch clearly did. This is my only concern.
I will have no issue with any career choice Poch goes on to make, short of joining Arsenal. If that job is offered to him it's safe to say that he's likely to have other comparable options, which anybody who values said 'code of conduct' (which he certainly appears to, given the comments you've referred to) would surely take up.
For the record I'd be utterly amazed if it ever came to that, based on my judgement of him as a person, so for me its almost certainly a moot point.