I think this could be a great idea, remove leveling up chars using iso and level up by playing time, like an RPG level system, so levels dont go up if you dont use them. I`m pretty confident that not to many people buy iso anyway, (maybe a few rich guy). This game needs a serious overall because it will be death in 6 months.
I think the ISO mechanic does not need to be replaced, but include alternate ways to lvl up a character. I and i think others have made the recommendation that extra covers should have the option to be sold for ISO or used to lvl your character up one lvl.
I know this would give me an alternate use for the 5 + cStorm/Ares covers i get weekly and would have a new fully lvled character in a couple weeks that i would never invest ISO in otherwise.