I agree. Allow characters to ETR anytime between 20 and 28 if they have 6 million karma in a sphere. There will still be a limiting factor to chain ETR's (Commendations), and once a character has expended all their accumulated karma they still have to earn another 6 million before ETR'ing again.
If people want to spend the turbine points to buy 3 or 4 hearts from the store so that they can chain ETR all their spheres, it's just good news for Turbine's bottom line.
I think this change would make both the hard-core 'grinding from 20-28 is a waste of time when I already have max karma and commendations' and the 'more money than time' players happy.