Not a good idea
TBH, employee representation on the board of a large company is not a good idea. Certainly not within the current legal framework around boards and board membership.
Having been on boards (of small companies) for the last 20 years, there are things that are discussed at the board level that need to stay within that context and not be known outside of it. An employee representative would be under pressure to break that privacy.
This is like putting a union representative on a board. Brilliant. The union now has information on the other side of agreement negotiations. How well would that work?
I expect to to be flamed for this, but the legal reality is that this would only lead to grief.