I like the idea, the bad part with increasing the moving mass though is even slower accelerations would be needed. Not that this wouldn’t work, just the first drawback I see. If you support the outer rails you could do away with the double rails out there and just do doubles across the gantry. So I think the best way to pull this off is basically build a box attach the outer rails on it (fully sported), the do your gantry.
Have a look at the updates forum and the V2 thread there are a ton of good Ideas in there. I am happy with the size and rigidity now, especially after adding the stainless steel rails! The only reason I could see doing this would be for a full sheet router….kinda cool!
Keep the ideas flowing I am finally catching up with everything here after the move so I will love to start a new project soon.