How can I build pull-down shelving for kitchen appliances?
I've always wanted to do something with a shelf attached with cables to pulley blocks with counterweights.  Kind of old school, but would do the job for you.  Using counterweights is good in your situation, because the weight of the empty appliance (microwave with no food) is constant. The downside is you must spent a good deal of time designing the system to the fit and finish of your kitchen. It looks like you can get the cable and pulley blocks from amazonsupply.com.