Describe the feature

For instance, a half pillar under a half slab to form a short T shape, allowing it to be a full block.

I bet you've added this and I haven't figured out how to do it.

Combining arbitrary blocks within a single block space will not happen. Both the existing and the upcoming double blocks are deliberately selected and they have specific code written for them so they work properly with the detailed face culling (hiding faces between two neighboring blocks when their shapes match).

If you need arbitrary combinations of simple shapes like your example, then you are better off with a multipart mod or something like Chisels & Bits.

Understood, thanks for taking the time. I really love this mod. I hope you keep it up ^^