No, I don't think I would tell a potential employer about a potential situation that might arise at some indeterminate time in the future. What would be refreshing would be if potential employers outlined at interview stage what their policies are in relation to their employees' maternity, paternity, parental and adoption leave, so that a potential employee has some insight into the company's stance on leave, and on what additional benefits or leave, if any, might be afforded to him/her. If I got the impression at interview that an employee seeking leave for family reasons at any time in the future would be viewed as hassle-y or inconsiderate, I would walk away and bring my talents elsewhere.
I think that many companies take a short-sighted view of maternity leave, seeing it as hugely disruptive for the 22-26 weeks that the woman is on leave, and tend not to consider the long-term value of the employer-employee relationship which may have already lasted years and may continue well into the future.