With the heroic mode event... I got the intuition that a new armor class will also be coming up soon... If it was not in the plan, here would be my suggestion:

New armor class: Heroic
max level: none. ( you can upgrade as long as you can... But gold cost always increase)

Another suggestion... Why not giving some properties to the capes other than the look... Exemple of properties a cape could grant to the knight who wears it:
- adds to armor power stat
- adds to armor defense stat
- increase chance to hit (lower misses)
- increase chance of a miss to oponnent
- adds a third element to an armor (possibly a bit too powerful)
- ect...