I thought about a system of forge components. Many kilns can be taken apart in sections; why not a horizontal pipe forge? Using Kaowool, the sections would be pretty much "gasketed" when connected. You could buckle them together with SS tool box type catches. You could offer blank rings and rings with a burner port. You could configure your forge to many different lengths and burner configs. (This is sorta like Ron Reil's sliding in/out back forge door.) If you made them say 4" sections with removable floors, the floor sections could be the size of a 1/2 length fire brick "split." That way you could cut splits in half, two 4x4's, and easily make and repair floor sections that way.
I like how quickly inswool heats up. It's lightweight to ship, and easy/cheap to fix. Think along the lines of the first volkswagens. Simple design, easy to fix in the field, cheap parts. I think it would be preferable to castable.
You could make buckle-on door sections with an inswool liner and either blank-no-door for the back, or with a small or large door for the front or for both ends. I like to be able to use brick for the doors. Once again, cheap, easy to find, easy to work with. When they burn up, get more. You can make an angle iron "track" for a brick door cover to slide in, but I like to just have a big front and back hearth plate that they can sit on.
As far as portability, I have made forges that sit in a light rectangular frame. This naturally holds the pipe body. The frame has tubing sockets for removable legs welded into the bottom at slight angles. I used rebar for legs to travel with; you can be a bit more polished than that. The frame has holes for a sliding work rest bored in it- you could make pipe sleeves with set bolts. I've been able to travel to demos with all my brick, hoses, regulator, forge, frame w/workrest, and leather apron packed into my tin washtub/slacktub, and the legs pulled out and stashed with the rest of the barstock. Simple and easy. When you get there, you have a free-standing venturi forge that sets up in about 2 min. and it's on.
A front work rest can be very handy. I would take a page from grinder design. You want simple, articulable up and down, in and out. Two pipe sleeves for in/out on the frame, two rods that slide forward through them, each with a vertical pipe sleeve welded to the end to receive the up/down sliding work rest end.
You could have a 10" forge system, an 8," whatever. You could make the body sections universal for vertical/horizontal configuration and blown/venturi burners. When set up as a vert. forge, you could make a "blank ring" with front and back side doors and blank no - door ends. Or the horiz. forge could be turn vert., with the floor merely being a pad of fire brick that the open forge body sits on. This is how I have my welding forge set up now. It's easy to fix or replace flux-burnt floor bricks.
Make the burner ports large enough for SS burner flares. Standardize the flare size between your comparable blown and venturi burners so either can be installed into the same port. Does Rex Price supply all of the burners for any forge makers right now? The T-Rex burners are real nice, perhaps you could use them or offer them as an upgrade.
Think about how a grinder is the one-tool-does-everything solution in many small knife shops. It would be nice to have a forge with this versatility.
There are many heavy-ass "indestructable ultimate fuel efficiency insane forge-welding heat" forges for sale out there. I'd go with a light design. It should be capable of forge-welding easily though, be sure you do insulate sufficiently. At least 2" of 2600 degree wool. I'd sell ITC-100 on the side for those who want it. I'm not impressed with Plistix 900F. I burnt it up. It's not reflective like ITC-100 either. You get what you pay for IMO.
Just my two cents.
