There are Kydex makers who don't use straps, and Alessi makes a rig where the snap is within the trigger guard and releases on the draw.
Although I make my own holsters in both Kydex and leather, I (personally) wouldn't make a passive shoulder holster; there's too much opportunity for your arm or body to 'pull' hard enough on the gun to release it, and the consequences of failed retention in a shoulder rig are fairly serious. In fact, the last shoulder holster I made for my G43 has a thumb break and extra molding, so the gun is fully retained without the snap; belt and suspenders, as it were.
Larry