According to Mojang, custom block geometry is exclusive to Bedrock Edition. The studio also mentioned that the feature will essentially give players the ability to create any block they can imagine.

Building something in Minecraft can take quite some time. Sometimes, one's block choice doesn't end up being ideal, and players need to swap their blocks for others.

Five free Bedrock add-ons that totally shake up survival, crafting, and provide some chaos. Best of all, it doesn't cost anything to freshen up gameplay this way.