There are so many things about this that feel bad. RE: being able to declare income from rent (that isn't anything to do with football) whilst not having to worry about the cost of it just seems to defeat the whole point of making the actually running of a football club sustainable. Instead, clubs are just encouraged to shell out loads of capital on any old venture that may generate them money, even if it is nothing to do with football or the club itself.
Secondly, I'm not sure NUFC can just decide to redevelop or repurpose the terrace themselves just because they own it—they'd need consent and I'm not sure it's a given that would happen. I also don't think it solves their issues about a right to light either as I beleive that goes with the property not individual occupancy of the building. It may be if NUFC try get the Council on their side then maybe those problems go away but otherwise I don't think their ownership of the properties massively changes things. If they start trying to blackmail the Council by threatening to leave all these properties vacant I'd certainly not respond well to it....
For what it's worth, I do think everything points to them intending to stay at SJP and trying to redevelop. This seems like quite a bit of effort to go to in order to keep options open. As Biffo said above, if they were serious about moving then there are much more obvious things they could/should have done by now. It would have been far easier to acquire an out of City site than sort out the purchase and all the issues above with the terrace. Yet, for some reason, they haven't...