New role advice

Background: I've been in my current role with a new employer for just over a year during which time my role has evolved and I am told my performance has been recognised.

During a recent reorganisation I was given a new role (which i am very happy with) at my existing grade as well being asked to perform a wider role for which I will have a dotted reporting line to my boss's boss. This was explained as being both to cover an emerging need and to give my boss's boss first hand experience of my work since they don't have personal experience (until the re-org my boss didn't work for them). I was informally told that their lack of first hand experience of my work was a major element in me not being offered a more senior role in the re-org. If I perform they implied that the dotted line would become a hard line and I would be promoted but in the meantime I have a larger and more senior role than my peers who have the same grade. I didn't ask for a salary increase at the time as I felt it would be unlikely to be considered and given the support of my boss's boss in a promoted role and the fact this is a growth company, the opportunity is more important at this time. My first question is whether I should have asked for a rise there and then. Not because I think it would have been granted but that failure to ask shows as weakness in some way.

So given this is in the past, going forward how do I approach the dotted line relationship and at what stage do I raise the subject of pay for my enhanced responsibility? 

I know the best time is to wait until I have demonstrated performance but I could argue that I am already doing that. Recognising promotion will likely bring pay rise in any case how or when do I raise the possibility of the dotted line becoming hard?

Sorry to focus on pay/promotion. The reason for doing so is that the company are giving me experience, training and opportunity and so salary is the only gap.

Thanks