What is the real difference between this and
If you live in Texas you should watch football.
Is that sentence subjunctive or indicative? You can look at 'should' as just another transitive verb. Right? It is the past tense of "shall", and we push it into the past tense to indicate the subjunctive. Well "ought" is an old form of "owe", indicating subjunction was part of the process of its formation in the past.
Either way, at its deepest intention, this is something beyond merely indicative, it is something else as well.
To the broader issue, I think constructions like these are deontological, but indicative in form.
- He owes it to them. (When this is not about money -- I am making a moral deduction.)
- You will do as the Good Book says. (I am either stating or enforcing a rule.)
- This is to be rectified. (It is your obligation to see to it.)
The question is whether my expectation is a real or ideal thing that exists, which is being indicated, or whether it is always a potential duty of yours, being recognize by me.
If you allow for the kind of idealism upon which mathematics is based, all told, I think the category of 'non-indicative' itself does not make sense in anything but a linguistic sense. In a world with mathematical ideal forms that can be referenced as real things, everything is indicative, and my also be deontic, or otherwise subjunctive.