It's a realistic expectation when they are engaged yes.
But before they are engaged? For what purpose? She can't attend family events. She can't accompany him on tours or official duties. If he is gone for days or even weeks on tours or other events, she does what, watch tv and wait?
Yes it is archaic. The 'if she is supposed to love him she should be willing to give it all up'. If Harry was Princess Henrietta, would we say the same thing?
If the princess in question happened to be the heiress to the throne, then I would say 'yes', see the examples of Daniel in Sweden, or Philip, Henrik and Claus in previous generations.
Otherwise, the answer would probably be 'no'. Still, I suppose the Swedish Royal Court for example
expected Chris to give up his career after marrying Madeleine and it came a little bit as a surprise when he did not and declined a title and Swedish nationality.
What needs to be remembered too, I think, is that should a marriage happen between Harry and Meghan, it needs to be an equal partnership and that means taking into consideration both partners. The days are long gone when a woman was the "little woman" and the man was head of the household.
Nevertheless, as senior members of the British Royal Family, Harry and his wife have a public role which they are expected to play. That is part of the "social contract" that exists between the Royal Family and the country and which justifies keeping the monarchy. Fulfilling those obligations takes precedence over Meghan's personal goals. For example, Meghan will have to give up acting and will have to live permanently in the UK. That is probably not negotiable and, in this sense, it is not an
equal partnership.
Going back to the discussion with Countessmeout above, the main reason why the same standard did not historically apply to husbands of princesses was that daughters of monarchs were actually
not expected to be working members of the Royal Family after they got married. In fact, most of the time, they were expected to marry into other dynastic families and usually join their husband's family / court.