Not entirely made up, we've seen early prototypes of them last year, we know they will be in the game, each with it's own casting method (Warlock will probably have somethign AED-Like and sorcerer with something similar to their 3.x incarnation), and we know Warlock subclasses will be based around the hexblade, binder and classical warlock with patron as another decision point, and we know that neither has ever prepared spells, moreover while the bard isn't a full caster, it is the only class that doesn't prepare spells so we know that will exist in some way. So no it isn't an entirely hypothetical matter, and while we don't know the specific implementations they'll have, we know of the trappings and problems non-prepared casters face when compared to prepared casters, moreover some of those issues are potentially greater now.