Unless it is a business requirement Zero Downtime is too expensive a goal to achieve. If it is a business requirement then a Cost/Benefit analysis can be done or at least some kind of business justification.
The complexity of a Zero Downtime solution is unlikely to be cost neutral and also unlikely to be without its own risks. As such it should not really be an internally driven requirement.
-- Stop your grinnin' and drop your linen...they're everywhere!!!