As I have stated elsewhere, my dream is to successfully unlock all troops within a reasonable amount of time with some measure of reliabilty/guarantee if real money purchases are made to attain said content.
So, here is one more suggestion from my wacky brain. Granted this would require a bit more work on the part of the devs, but…
What about Troop Mission Packs that are purchased with Gems?
This would be a series of battles akin to the regular campaign, or class unlock missions which reward you with a specific troop. To address issues of longevity the “Battle Master” or whatever in game character offers these “hunts” will not speak to you until you have attained lvl 150, or WL4. They are a one time mission and only reward a single copy of the troop.
Just to throw some numbers out there I would suggest:
A Legendary Hunt= 500 gems (450 is 50 gems keys which at 2% should reward 1 legend, but extra 50 for guarantee)
An Epic Hunt= 400 gems (for those hard to find unique kingdom epics)
This would assist loyal players with unlocking all troops, encourages the ingame economy by requiring use of gems, avoids early power gamers by stipulating that they are too weak to hunt these legendary beasts, and it would create new fun ways to see old friends and their witty dialogue! I can’t wait to see what Tyri and her brother have to say when I ask them to help me track down ANOTHER Giant Maw! 
Thoughts, opinions, suggestions welcome…