Although sustainability is important, and very important at that, it is not as big an imperative for some companies as it is for others.

For a company where issues of sustainability and environmental responsibility are critical or important, one might consider having those skill sets represented on the board. But similarly, sustainability skills can be bought through the advisory market for those companies where those issues aren't critical all the time.

Similar arguments can be made for legal, financial, industry, international, people, technical, etc skills for different companies.

Ultimately, the skills represented on the board must be the skills that help the board steer the corporation - no more and no less. Too many companies have adopted guru theories and trends and have been burdened with non-value adding processes and disciplines.

Let's be careful but diligent about which skills are represented on the board and why.