I think* that it would not be too hard to add -50% and -75% as a counterpoint to the bonus XP available from START (nee P2W). And, assuming that it is easy, I see no harm in adding that as a choice. I could even see it adding bonus Inf, like the boosters trade XP for Inf, but turned off at level 50 as well.
I also want to remind the OP and others that might see this that players can choose to add difficulty settings to any TF or Ouro arc. You can buff enemies, debuff yourself and teammates, remove benefits of enhancements, prevent the use of inspirations, and limit powers in several ways (no power pools, no temporary powers, no travel powers, and/or no epic/patron powers).
Edited to add that I don't like the badge portion of the OP. Making new badges that my old badge collector could not obtain is a non-starter for me.
*Insert Standard Code Rant