I have a debit card on the way, and want one for my wife too.
Sure, she could open up her own xapo account and apply for a card, and we're willing to do that.
But if there is no way to link those two accounts together, so that they have a shared balance, it becomes too much of a hassle.
Let's say her account holds 300 dollars worth of bitcoin, mine 500. Neither of us is able to buy something with our card which costs 650 dollars.
But if the two accounts had a shared balance, we would have 800 dollars. See my point?
The way it is now, we would have to move funds before making said purchase, which seems inconvenient.
I see your point, and that would be a nice thing to implement in the future. Having said that, the great thing about bitcoin is the ease of transferring funds. It would literally take seconds to transfer the needed cash from your BTC address in Xapo to hers, so that's not a huge barrier at this moment. Additionally, we do have multi-user wallets. While you can only have one card per account, you can create as many secondary wallets as you want, and they could require permission from all parties in order to withdraw from it.