IBM invested *heavily* in ECL (A.K.A. CSEF) with one deviation into TTL (one series of mainframes) in the late '70s before CMOS finally buried it with density. ECL at those densities would be impossible to cool. As it was they spent a billion bucks on cooling/packaging to get as far as they did (early '90s). ECL is fast but not nearly dense enough to be usable for anything other than boutique parts (clock generators and such), today.
If you think there was no investment in ECL, you're quite mistaken. As far as twisted pair goes, no problem, though not needed. Single-ended microstrip works just fine. Even standard wirewrap, against a ground plane, was used for decades.