One potential problem to watch out for with open dated tickets from my expereince:

If you have an open dated coupon A to B and oneworld airlines stop flying A to B you need to reroute (and pay the fee for this).
Same if you have a coupon with a date, want to change and no airline is flying that sector (any more)
If you have a dated coupon and because of a schedule change nobody is flying any more you are protected.