Well, the very first thing I'd say on Mythic equipment is that, for casual (specifically players that will never check the forums here) players they have to spend who knows how many mythstones to learn how to make one of the mythic items, then they have to spend (scores of) hours to get the mythstones to create it.
Then, even after knowing the list, there's not having the necessary wide selection of mythstones available. And/or not having enough of the very-high-rarity mythstones to create the Mythic items. Mythstones are far rarer than crystals, by a long shot. I'm close to completing the "Find Crystals" feat for the third time while nearing completion of the "Find Mythstones" for the second. (Note: This ranges from 1.7 to 1.7.1 and to 1.8.)
Tacked onto all that is not knowing whether the entirety of the opportunity cost is worth it for the end product. Mythic items have special effects and abilities, but there's no other way to see how they play out with a particular play style than to actually craft and use it. And to create a mythic item, the player has to have the right piece of equipment with at least four sockets on it.
I think I would rather the four required mythstones be transformed into the mythic item, carry the former mythstone effects as affixes, and have two sockets for the total of six affix spaces. That would continue with keeping the item's versatility very much alive, continuing the pattern of all the other equipment.