Metal looms and shields have been used for a long time by car makers. Buick had steel covers along side the heads on their V8 Nailheads which covered the spark plugs and wiring boots. Chrysler ( ? ) had a fan shaped loom on top of their flathead 6's. There are probably several other examples but those 2 come to mind at the moment. When you consider that they were running plain rubber covered wires with slipped on boots it is a bit amazing they didn't have more grounding and cross firing problems than they did.
Today we have silicone wire insulation and factory sealed plug boots that are superior to stray current leakage. If you did want to run metal looms you would be better off than grandpa was with his Buick or Mopar but I agree with AMC that it might be asking for trouble eventually.
That loom pictured does have some eye candy appeal to it if that's what you are after and done right may never be a problem.
