I am sure one could be fabricated from CF or Kevlar. All depends on the engineering design and skill implemented.
Note that car is running Alpha-N (or something similar) engine management. The AFM is removed. The engine management question is one to consider...keep the stock MAF and Motronic DME or go to a MoTeC or Autronic DME system.
Also keep in mind the resonance flap on the stock plenum...loss of that could be detrimental.
...not to mention you will need it to be expertly tuned, no-one I know has done this modification, I rang a good tuning company up a few months ago regarding exactly this, they had only done it on the M3, and said they could "probably" do it on the M5 3,8. I dont know about you - but "probably" aint good enough - he also mentioned a higher fuel consumption and loss of driveability.
Kempower - promised they would have a system tested and developed - ready to sell by September. I have e-mailed them to see how it is going if anyone is interested. I dont think I will go for it, but I will certainly relay any communications from them to you all.
I can't see the point in giving up the multi-path plenum on a street car. The potential top-end gains are not worth the loss of low-end power... and accepting the opposite means you should trade-in on a 540i and be done with it.
The factory M5 airbox is remarkably efficient, especially with the venturi lip. I may be doing some experimenting with an alternate (yet similar) design put together from our Viper components. While the component quality is top-notch, I will be the first to express genuine surprise if we get significant results on the E34 M5. The OE airbox is really just that good.