Why go for a road disc rim? Any 29er rim with the right internal will work. I got WTB i-21s on my disc build. 440g for £40. 21mm internal which I'd happily use 28s for (cant remember what tyre youre planning on using for this)
With a wide internal and wide tyre its unlikely you'll be using 70+psi. Most 29er hoops will be fine with that. People have even run 80 in Stans Crests which are only rated to 40psi or something
Why go for a road disc rim? Any 29er rim with the right internal will work. I got WTB i-21s on my disc build. 440g for £40. 21mm internal which I'd happily use 28s for (cant remember what tyre youre planning on using for this)