You'd think everyone would do this, but I'm not sure they do.
DH and I did not. He's a reasonable man and whilst inclined to do the minimum has always made sure he pretty much pulled his weight, so I expected no issues. We'd agreed I'd have a year of Mat leave then we'd figure out the childcare.
It went fine! We pooled all income, never any issue over what I spent even when I was out of paid ML. When I finally went back to work we both went PT with a bit of family help to cover childcare. Free time split pretty evenly. Time doing childcare not so even because ND toddler wanted me but it was never left all to me. Housework more me than him but not ridiculous. Mental load nearly all me until I realised after many years that that was wrong.
To me this seemed the obvious way to do it. I'm always surprised when I read about the mother being expected to still pay 50% of bills on reduced salary, or being 100% responsible for organising 24/7 childcare (with dh 'babysitting' his own kids whilst she runs to supermarket on a Saturday) or getting no free time while he plays golf twice a week to unwind from the BIG JOB which pays the mortgage.
So, did you discuss in this level of detail? Or is it unreasonable because nothing ever goes to plan anyway?