In terms of epic scaling for the eldritch blast, has it been considered to give it an extra d6 for every so many epic levels? You could grant them automatically if you have levels of the warlock class in the same way you do for melee and ranged power. Another is to have the blast improve the rate at which is scales with spell power based on the number of epic levels the character has. A third option is to give the eldritch blast a bonus to damage based on the warlock's Cha modifier.
I am not sure which one of these would be the best choice, or the rates of which for each (would likely need a fair amount of testing) but one of these, or a combination there of could help or solve the problem of scaling.
As a side note, do other arcane classes have spell scaling issues in epics? If not, what do you feel the difference is between the existing epic classes and the warlock's eldritch blast?