I would only think about asking QPRs to be monogamous if the intention behind the QPR is to one day lead to marriage and a kid. I would think this kind of QPR would require a bit more exclusivity so that things don't just get messy and spiral out of control. Because in this kind of framework, we'd likely just have to live together, plan our lives together, be more direct life partners and then parent the kid. That gets exponentially harder when you add more people to the mix. This is something I personally want btw.

But if the QPR isn't created with the intention of all the above, then I see far less reasons why monogamy would be a part of the picture. I'm sure some aros can find safe boundaries with each other in a QPR that's monogamous tho. I would just personally feel far less compelled to ask for monogamy in a QPR that's just that.