Well i just thought of it right now.
Hi, welcome to the forum!
We have the ability to make custom C-shaped blocks, or E-shaped, or more!
As for hat blocks, what we have instead is the "generic hat block":
You can put any test you want in the hexagon.
No, i meant the "Make a block" section
the problem with that is that you can put multiple c-blocks on a block, and the blocks in the c-block are used as a value, so that's never happening.
Hat blocks are another thing. Adding a hat block shape in the make a block section is more doable than c-blocks, and I kind of wish they added the hat block shape to custom blocks.
Ok then! Let the C block go, and make the hat block thing happen!
yeah, but I'm not a snap dev, so I can't decide if they add it.
Got it! 
How do you make snap blocks in the Snap forums btw?
you can't make snapblocks from text in the forums, so we just use images. Right click the block and click script pic, then click on the image icon (it says upload if you hover your mouse over it) then click from a file and then upload the image.
... or just drag the picture into the forum's editing window.
So, you want us to open a block editor with a generic when block in it, and you're not allowed to drop blocks anywhere other than the hexagonal input slot?
We get this request once in a while. But I'm not sure what it would add to expressiveness, and it certainly wouldn't make anything possible that isn't possible now, so it seems pretty low priority to me.
now that I think about it...
Nevermind, now that i think about this, this ain't gonna work, how do i delete my forum post?
Nvm i figured it out.
Dang it error!
I don't think it should be deleted because other people would be able to learn from this
Ok!
There is a FAQ post about this.
There is now; I made it in response to this thread.