The introduction of a membership fee by Travelzoo is a significant change in its business model that could lead to increased revenue from memberships. However, the impact on the stock price is uncertain as it could also lead to a decrease in the number of new members or loss of existing members who are unwilling to pay the fee. The announcement includes a waiver for new members who join before the end of 2023, which could lead to a short-term increase in membership before the fee is implemented.