Alpine bindings have excellent release mechanisms for their main use in ski resorts. You can add Alpine Trekkers to these bindings that allow you to free your heel for skinning up. If you ski wicked steep and rocky terrain the weight trade off may be worth the beefy support, but alpine ski boots have slippery soles and are not comfy for hiking. This also complicates step-kicking. Free-heels suck when the snow and terrain aren't forgiving and this can be a safety issue in avalanche terrain.
Voile also makes releasable tele-bindings.
You can use alpine ski boots with these bindings, but AT boots are softer and lighter. Since both legs are on the same plank, twisting injury would seem unlikely for a locked-in rider and most riders seem to believe that the possibility of untimely releases is more dangerous than no release at all. Unfortunately, this doesn't address the danger of deeper burial in an avalanche. Some riders rig cords at their waist and down their pant legs that they can yank to release, if necessary. Some of them will niftily screw onto the ski pole-probes I just talked you out of.