The problem you will get into with an ultralight polymer revolver in .38 Special or .357 Magnum is recoil will be difficult, at best, to control.
For example, take an extremely light revolver in .357 Magnum, and a 40 ounce Ruger GP 100 4.2" barrel in .357 Magnum, and have them shoot full house 158 grain loads. In the GP 100, they are manageable. In the light gun, they could break your wrist with recoil. It happens with .44 Magnums also; short barrel light .44s recoil like crazy, but longer barreled, heavier revolvers recoil less. Simple physics at work here.
The smallest revolver I own is a Model 85, and that is about the low limit in gun size for .38 Special I will endure. Now I have a Ruger SP101 3" barrel that is the minimum weight for .357 Magnum loads I will use. I have shot a S&W 340PD with 125 grain JHP ammo, and that was not fun at all. The recoil alone was brutal to the hand and wrist.
Personally, I do not see a need to put a super lightweight revolver together with a powerful cartridge just to do it. I have tried it with another brand, and it is not something I care to deal with ever again.