If you print a red 3/3 first strike haste like you suggest, that messes with the Standard format. You can't print new cards that bypass Standard.
I've discussed this in other posts, but of course this thread is completely separate so I will clarify here. I said nothing about printing Standard cards. Commander, Archenemy, Planechase and any other future variation of "special products for non-tournament players" are perfect places to put powerful Eternal cards for non-blue (and non-artifact) mages. In the past, I've advocated for printing Eternal-relevant cards that would be too strong (or too weird) for Standard in these special sets.
As a sidenote, Reckless Waif and Monastery Swiftspear are examples of two cards that can function as highly powerful red one-drops. However, they aren't permanently switched on the way delver is once it flips. They also aren't in a color that isn't supposed to get insanely efficient threats to begin with. If they printed a green instant for one mana that countered any non-green spell, that would be the equivalent of Delver of Secrets. A black 2/2 zombie for one mana that destroys an artifact or enchantment when it comes into play might be another example.