First of all, I am against allowing an Epic Character to multiclass into a new class and take Epic Feats as Bonus Feats.
A 20th Ftr / 20th Bbn has so many feats, a certain number of which are possibly Epic.
A 20th Bbn / 20th Ftr has the same number of feats, but 1 more Epic feat than the character above.
If an Epic character multiclasses into a new class, he is stuck with the non-Epic Bonus Feat list until the new class is also Epic leveled.
All that aside, I think multiclass characters can be viable at Epic levels assuming they are created intelligently. Their regular feat every 3rd level can still be Epic and they are still gaining lots of bonuses each level (more and better spells, more SA, more FA, more Rages, more ... well you get the point.)
A 20th Ftr / 20th Bbn has so many feats, a certain number of which are possibly Epic.
A 20th Bbn / 20th Ftr has the same number of feats, but 1 more Epic feat than the character above.
If an Epic character multiclasses into a new class, he is stuck with the non-Epic Bonus Feat list until the new class is also Epic leveled.
All that aside, I think multiclass characters can be viable at Epic levels assuming they are created intelligently. Their regular feat every 3rd level can still be Epic and they are still gaining lots of bonuses each level (more and better spells, more SA, more FA, more Rages, more ... well you get the point.)