Philosophically, I think it's a couple's business how they divide their responsibilities between earning and working in the home, and the tax system should treat them as a single unit.
I would extend this to tax on investment products as well: currently, virtually every serious product (available to the masses i.e. not custom family trusts etc) is in a single person's name. For example, there are barely any joint savings accounts that pay a decent interest rate, pensions/ISAa are in individual names etc.
If there were a simple way to tax jointly, I think more of these products would exist.
Why do I care about this? Because I think it would solve quite a lot of the issues that come up on MN w.r.t. money in relationships - "you can't take a 3-year maternity leave, or if you do you need to beg your DH to donate to your pension".
I don't think it's enough to just be able to inherit someone else's pension/savings - beneficiaries can be changed. I think throughout life, many couples would like to truly manage their finances jointly, but the tax system and types of financial accounts available don't make it possible.