Now that the luck elixir was introduced, maybe a new elixir could be added for those who cannot gain XP anymore.

Maybe something similar to the Thrasher elix which offers speed, attack, defense but remove the standard luck pot and the XP pot... and replace them with the new super luck pot. Since the XP pot makes up roughly half the cost of a thrasher, it would be nice if it were slightly cheaper than a thrasher, but even at the same price it would be more useful to capped chars.