With thinner mirrors and sensible use of materials a 14 or 16 inch dob doesn't have to be too heavy. Once you go much past that though unless you use lots of exotic materials and are prepared for a very stripped back experience it's extremely hard to not end up with a heavy scope, just the mirror box alone will be heavy and hard to handle. Some of the creative approaches (string scopes, lots of carbon fiber etc) also don't really scale big. The mirror ends up being the most significant weight anyway.
This book is worth the read if you are seriously interested in this area -
https://www.amazon.com/Engineering-C.../dp/0943396956 - Of course it just got harder to buy with William-Bell out of business.
I've had the privilege to look through many very big scopes and while you do get a little more on a really perfect night I'm now pretty much convinced it's rapidly diminishing returns after about 16 or maybe 18 inches. The extra effort involved in moving, setting up and observing up a ladder doesn't justify the improvement. That ignores the inevitable thermal equilibrium issues and flexure inherent in larger scopes.
On the earlier suggestion of an aluminum mirror it wouldn't work well, we need materials which are very thermally stable for mirrors - hence the shift to quartz vs pyrex at the high end.
If money were no object - a big CDK (or similar design) on an alt/az fork or L style mount in a dome would be the most comfortable experience - fairly consistent eyepiece height and position, feet firmly on the ground and a comfortable experience. Things to dream about.