TL;DR - Because of how flywheel energy storage scales it is unlikely that significant efforts will be made to develop the technology for home use.
This is similar to the case for windmills, where the power output increases as the square of the diameter, and the cube of the wind speed (which itself doubles roughly every 20m of elevation).
From the Engineering Toolbox, the equations governing flywheel kinetic energy are:
E_f = 1/2 × I × ω²
I = k × m × r²
E_f = flywheel kinetic energy
I = moment of intertia
ω = angular velocity (measured in radians/second, proportional to RPM)
k = inertial constant (a value from 0 to 1 which depends on the flywheel shape)
m = mass of the flywheel
r = radius of the flywheel
If we were to assume all flywheels have the same shape, roll all the constants together in to some value
K, and combine the two equations, we'd get something like this:
(flywheel kinetic energy) = (K) × (RPM)² × (mass) × (radius)²
Thus to maximize the energy storage of a flywheel we would focus on making it larger (increasing the radius) and faster, as the total energy will increase proportionally to the square of these factors. Note from @Ghanima's answer we know that efficiencies are already greater than 90%, so there isn't much potential there.
- double the radius, quadruple the energy
- double the speed, quadruple the energy
There's a fun calculator you can use to see this in practice.
For domestic applications, making things larger is not an option -- it has to fit in a home. Thus to advance the tech for home use, designers would have to increase the speed.
Increases in speed are limited by technology costs and electricity supply -- faster motors cost more, and require a higher current input than may be available in a typical home. Given that energy potential increases for this application are already limited by size constraints, it simply doesn't make sense to put more money into the motor and the electricity supply.