If we get an Unown pre-evo, then an evo is positively neccessary for those worthless Pokemon.
To get the pre-evo (I like Prince of the Seas idea so let's call 'em Unnites) you'd have to have an Unknown and a Ditto in the Day-Care. Similar to Manaphy, the Unnite that is produced won't evolve into an Unown. This keeps the novelty of the Unown being "legendary" while giving us lower-case Unown.
The evo would be more complicated. Let's call it Orikey (Original Key). To get Orikey, you'd have to have successfully captured an "O" Unown, and bred an "r", "i", "k", "e", and "y" Unnite. Then, you'd organize them in your party in this order: 1st slot: O, 2nd slot: r, 3rd slot: i, 4th slot: k, 5th slot: e, and 6th slot: y. With your Pokemon in this order, revisit the (example) Ruins of Alph. There, the Unown and Unnites in your party would "react" to the area's psychkinetic energy and cause them to merge together to become Orikey =)
What'cha think?