A theoretically neat solution but........
Using the flip top as one sided creates useful bench space. However to rotate the flip top you would need to fight the weight of the machine.
Using the flip top for machines double sided means that at least one of the machines would need to be less than about 11" high or a 24" flip top bench will need to be placed away from the back wall, possibly eliminating any space saving.
In both cases the basic proposition is that the height of the bench works for both the machines and (possibly) hand work as a bench. Any dust extraction would need to be refitted after each rotation.
Overall I think this may be a solution only for small machines of fairly similar weight with flexible height needs - eg: bench grinder and belt/6" sander
Terry