Rather than filling every deck with banal responses, it is preferable to allow some flexibility in the composition of a deck.

Players may bring a 10 card sideboard in addition to their 99 cards and 1 Commander.
After Commanders are announced, players have 3 minutes to make 1-for-1 substitutions to their deck.
Any cards not played as part of the deck may be retrieved by "wishes".

Reasoning:

Highly tuned threats piloted by skilled opponents mandate efficient answers. The minimum number of response cards required to ensure they are available in the early turns can easily overwhelm the majority of an EDH deck's building space.

Sideboards allow players to respond to the "best" strategies in a timely fashion . They should be strongly considered as a necessary defense against brokenness and degeneracy in an environment where no gentlemans agreement on style of play exists.