Glad to have you back after the wind-fest MC.
When discussing better/stronger/faster Remolino-width rims we may need to re-examine and re-evaluate some basic material concepts in order to make significant advances.
Just to get everybody on the same page, discussion-wise, I'll assume that people have reviewed Scot Nicol's excellent series on basic materials characteristics:
http://www.ibiscycles.com/tech/materials_101/ He may have had frames in mind when writing it, but it should be required reading for anybody wanting to get into a discussion regarding materials usage in bicycles, period.
With that in mind, we need to consider the challenge at hand, that is to say how to go about designing a rim that could improve upon those currently available from a performance standpoint, but that would also be economically viable to produce and market.
Initially rims were made of wood. It was lightweight and people had experience working with it. When using a fixed gear and/or friction brakes acting on the tires there were no concerns about rim wear from braking, and with tubular sew-ups the need for a precise interface at the tire/rim junction was minimized. No need for thin bead hooks or airtight seals.
Rim brakes and clincher-style tires presented challenges that wooden rims were not in a position to answer, so the industry switched to metal rims. Steel works well from a strength standpoint, but forces compromises in the areas of weight, corrosion resistance and braking friction. The density of steel demands thin wall sections in order to bring the weight under control, but they soon become too thin to, A) be durable and B) provide a braking surface with any sort of wear margin. Unprotected steel (other than stainless) can provide a great braking surface, but it rusts. Coating the steel with paint or plating prevents rust, but sabotages the frictional properties of the braking surface.
Aluminum addresses those problems by being both less dense than steel (which allows thicker cross-sections without being too heavy) and having fewer problems with unsightly oxidative characteristics. Various alloys of aluminum (in combination with other metals) provide a combination of basic material characteristics that make them a very good choice for most rim configurations of somewhat normal size and usage.
That being the case, two fairly recent developments in the bike world have stretched the envelope of desired performance characteristics beyond that which aluminum is in a position to answer. These needs may come from opposite poles of the cycling spectrum, but they have provided a synergistic impetus to the next wave(s) of rim materials.
The development of rear suspension on mountain bikes presented a number of difficulties for the mounting and positioning of rim brakes. That, in combination with increasing demands upon braking performance created by a greater emphasis on fast downhill riding and racing has pushed the development and deployment of disc brakes on bicycles. As a result of the proliferation of lightweight and effective disc brakes, rim manufacturers can now design rims free from the demands of functioning as braking surfaces. So far on mountain bikes this has primarily played out shape optimizations that allow enhanced strength/weight ratios rather than changes in the materials used, but carbon-enhanced aluminum has recently appeared as a rim material and I am sure that we will see more of that type of thing from more manufacturers in the near future.
In the road world many manufacturers have been forced to look at lower-density alternatives to aluminum in order to reduce weight and/or increase the volume of the rim in order to improve aerodynamics. Some have gone with aluminum rim structures with composite fairings, some with carbon structures with aluminum braking and tire interfaces, and some with all-composite designs. Designs using carbon braking surfaces may work satisfactorily under clean and dry conditions, but the wear characteristics in less than perfect conditions can be cause for concern.
So where does this lead us? I believe that as rim widths in the MTB world rise, the use of composites for the basic structural core of the rim becomes progressively more attractive. The fact that one can specify the use of non-rim brakes is no longer a negative issue for most (sorry G.P.) but there are still some issues with respect to real-world durability. Composites can be very, very strong, but certain metals and plastics have advantages when it comes to rock damage resistance and such.
I have yet to see this, but I believe that the best way to get the ideal combination of high strength, acceptable durability and significantly lower weight than the Remolino and Large Marge will be a composite rim with externally armored flanges. The armor could be a thin stainless steel sheath or a thicker thermoplastic (think bash guard) layer. It would only need to be applied where necessary to protect the underlying structural composite from rock damage. The armor need not be thick enough to provide structural strength, it should simply protect the surface integrity of the underlying composite.
While an 80mm rim might be the ideal application for such material in order to provide tha maximum possible weight savings, it would not surprise me if the same combination of materials could also be used to good advantage with DH rims greater than 36mm in width as well as for deep-section CX rims for use with disc brakes. Why not deep section aero DH rims with shorty bladed spokes?
Remember, you read it here first!
