It has been said several times now by various people, including Ceoli, the OP, that we are not talking about personal boundaries for an existing relationship like "keep me updated" and "we should maintain our regular date night when you start dating someone new", we are talking about rules that an existing couple places on the behaviour of/with a new partner, possibly even a person who does not yet exist, such as "I don't want you to develop strong feelings for anyone else but me, so if you start dating someone new, you will be limited to the number of hours you spend with her even though you haven't met anyone yet and she isn't here to give her own input on how much time she wants to spend with you".
So then it's just the sentiment behind the rules that's the problem. If a couple was to have a guideline saying that except for Saturday evening we need to be able to rely on each other to be there to get the day to day things of life done; that would be ok. But saying you're only allowed to see a new potential partner once a week because I'm worried about how it will affect me isn't? Seems to me that it all really boils down to the same thing and that it's only the wording that changes.
For example I do rely on my partner to be there to help me out with the day to day stuff of life and I do worry that if we don't have that time together that I will suffer for it. I'm not worried that his affection for me has changed but the stress of dealing with the day to day stuff of life while he is free to date someone as often as he wants would build a resentment in me which would be bad for us. So it does seem to me that it's all about the wording.