Well, unless the roles of supporting charities and visiting communities id drastically reduced, the "spares" can have long careers of duties. Princess Anne and the Wessexes are core working Royals after all. And Harry chose not to be (rather than there being no role for him)
So I think the DC of a monarch could well be working Royals, even under a slimmed down model, but not their DC unless in direct line - which isn't that different, as only W&H became full time working royals - so they are the ones who need to be prepared for an independent life. And if that's the case, should those outside the direct line have royal titles?
And if it's going to be aristocratic titles, for non-direct DC, then I think both girls and boys should be ennobled and in forms that are inherited by oldest child regardless of sex. I don't think male primogeniture on aristocratic titles will be abolished, but new titles don't have to be set up that way