Using Electric Motor/Generator Instead of Inverter to Deliver AC Mains from Batteries / Solar
What you are talking about is called a motor-generator set. The idea is well-known and has been used widely, although not so much for DC to AC conversion. Compared to solid-state inverters, though, they have a number of problems. First, mechanical wear and maintenance are a major factor in operational cost and reliability. Bearings and brushes wear out. Second, locking the output frequency to the line frequency to allow co-generation is much easier with inverters.

For private use, a motor-generator is simply not a good idea. Not only is it more expensive than an inverter, private home-owners are not likely to perform the periodic maintenance (especially lubrication) that the system will require. When the system then fails, your company will be blamed for providing a shoddy product.