You're contradicting yourself, OP. When someone is rich, it doesn't matter what he has in his possession to get wealthy; being rich is being rich, thus the comparison is unnecessary. When you suggest they'd be the only crypto-rich people in the world, the mentality of 21m bitcoin being owned by 21m couples after all have been mined is likewise unrealistic.

As you mentioned, the value of bitcoin fluctuates, and there is a lot of anticipation that the price will be higher than it is now when the last bitcoin is mined. To me, if 1BTC is valued close to a million dollars by then, owning one-third of it will still make you wealthy in certain parts of the world.

Note: Not all riches come with all the pleasures of life; some are a burden you can never get out of and will regret for the rest of your life. So marriage should not be intertwined with riches; they are distinct in their own right.