David Weaver
I'm not much of a user of coffin planes, but when I made a few, I thought it would be nice to have one with the insides made like an infill plane (the wear in front of the iron falls away rather than back toward the iron).

I made this smoother out of purpleheart, excavated the area in front of the mouth and made an insert to achieve this. It works great.

Unfortunately, the berg iron that I have for it isn't that great (it's chippy), and I haven't addressed it.

Of course, you couldn't make a plane like this and sell it (it looks like an old beater plane from the bottom and the insert is fixed - not a fan of screw held inserts for various reasons - so it doesn't look intentionally made like an adjustable screw-held insert would be). But, you can make a plane like this and use it!

This purpleheart is almost dense enough to sink - the coffin smoothers I've liked the most are made out of denser wood so that their weight is closer to metal smoothers (I don't work much softwood or mahogany where the lighter beech smoothers might excel).