A lot of advice I've read recently makes the excellent point that if you didn't manage to get a pre-nup, you may still be able to get a post-nup.

I've no plans to divorce any time soon, but I would like to get our finances into a position where, if we decide to separate, all the math is already done. I don't want my status as a provider to be the thing binding her to me, nor do I want her disproportionate claim on my wealth to bind me to her. I believe creating this situation will (paradoxically, in the BP world view) make the marriage stronger. Think of it like a nuclear button either of us can press at any time.

She has been a housewife for some of our marriage and earns considerably less than me. She will be starting a new career soon and has ambitions of starting a business later on, in which I would effectively be an investor. What I am hoping to create is a framework where she can claim a share of our accumulated wealth up until this point in the marriage, and take responsibility for that share from now on. Of course, I shall still be providing for her, but in the form of shared expenses (rent, holidays, etc.). The rest is up to her and her career. It should also remain the case that we both benefit from and are incentivized by each other's material success (and sacrifice, in some cases).

There are no children and we don't plan any, so I'm hoping the form this could take is roughly, "what would our finances look like if we hadn't married and combined everything?" balanced against "what percentage of our present wealth would she need in the event of a separation, in order to be able to be comfortably independent and thereby not unduly bound to me by money?"

Has anyone done anything like this, in the context of a functioning relationship rather than a bitter divorce?

Is there any useful rule-of-thumb I can lift from divorce case law?

Note that we're not in the US (we're moving there soon but still won't be subject to US divorce law unless we were to jointly decide to divorce there). That said, for obvious game-theoretic reasons I can't expect anything that's a significantly worse outcome for her than a no-fault divorce in the UK or Japan... and she can't expect anything that encourages me to limit my losses by divorcing now purely for financial reasons.

If I manage to develop this idea into something re-usable, I'll be glad to write it up and share a spreadsheet!