If you can make a machine that has the capabilities to do the following, I will buy it and so will many others.

Constant Current ACHF Squarewave GTAW 250 Amps
Constant Current DC GTAW HF start      250 Amps
Constant Voltage  GMAW with the ability to produce spray transfer with .035 ER70S-6 filler metal  (200-210Amps at 400 inches per minute wire feed speed)  Also an short circuit mode inductance setting that is either adjustable or favorable for open roots.

Smaller is always better, but if it can do squarewave AC GTAW and CV GMAW both, you will have a tool that NOBODY in the U.S. currently markets...  I suspect they would rather sell two machines, because the technology to do what you describe has been around for 15 years.

Also:  If you would like an American to test your prototype model, allow me to be the first to volunteer !

I will test it
and have the young starting welders to try it
I would like something like the diahen dw300 mig with wave and pulse ac/dc
and a gtaw like the lincoln invertec where you can adjust the wave from sine, triangle, or square
hope this helps
sincerely,
Kent

First off, if you're going to have 250 amp AC/DC then you also have the capability to have 250 amps AC/SC for SMAW (MMA)...
The next question is @ what duty cycle will the machine be capable of @ highest amperage? The same question should also be asked for the GMAW process and the Plasma cutter as well... What OCV will you be using?

Where will this machine be built? I could advise you in selecting the most appropriate components of both electrical/electronic and other non-consumable parts also so you don't end up designing a machine that breaks down in 30 days or less and instead last up to 20 years or so!!! 

You should also design it for single and three phase power input because you will in effect increase your potential customer base.
Why? Because quite a few of the small (This also depends on your definition of small!) shops run on 3 phase power and the same could be said for some DIY"s as well!

I would also agree with Fixalinc in designing a machine with substantially more current output and I would say 400 amps @ a minimum of 60% duty cycle would be acceptable for purchase amongst a very large share of the market along with @ least a 5 year warranty also! Okay! How about a 3 year warranty @ minimum... I'll even real world test it out for you to find out if you designed a machine that will be very desirable to just about everyone looking to purchase you machine!

Respectfully,
Henry

rethought this.
your best people here are
Lawrence, Dr. Crisi, are both teachers and welders
next are Dwanye aka Cactus and Stan aka Hillbilly both run shops
if you want the best it is Henry
DAMN now I can never be a CWI........someone might be better than meroflmao
sincerely,
Kent

It does sound like a small fabrication machine because it will not run heavy SMAW electrodes well enough for real pipe work and does not appear interested in any arc gouging either. But even for shop fabrication I'd want spray arc voltage available in CV. At least 32 volts?