Saw a cute thing at the "Havana" OpenStack Summit: a Dell ARM prototype. It is based on C5125 module for C5220 chassis. If you go to Dell website and check their gallery, it's readily apparent how busy the design of the x86-based module is when compared with the ARM (the x86 is AMD; Dell have an even worse module based on Intel -- 50% thicker).
Another thing, I love the way drives are bunched on trays. People keep chasing the individually accessible drives with the corresponding hit to density. If one abandons the hot-swap mania, he can do these nice trays. Also! This is the first time I see someone intelligently using the 2.5" drives. Only took 15 years. About the only critique I would level on the thing is that the air goes over the drives in sequence. There's a bit of spare width for staggering, so a few cheap baffles and/or raisers could even it out, but someone at Dell decided not to bother.
BTW, Dell people told me that the prototype is not slated for production. They are waiting for the 64-bit ARM. Typical. ARM servers are always one year away, for many years now. In the time we heard promises of ARM servers SpaceX built whole rocket and started launching it, but Netwinder seems harder to reproduce than Saturn V.