I remember reading about the PCI bus, which I think is the first time I heard of a mainstream digital system requiring serious transmission line design.
Actually, one of the selling points of PCI in contrast to competing standards was that it was significantly easier and cheaper in terms of transmission line design due to reflected wave switching (ie. no termination), this essentially means that only the steady state is relevant for signaling. While not good practice by any measure, this means that PCI bus does not have to be physically an linear bus, but works with arbitrary trees that does not contain excessively long paths (see for example aftermarket right-angle multi-slot PCI brackets for SFF and rackmount systems, that bus most of PCI signals for multiple slots together and only break out REQ#, GNT# and IDSEL through few wires to other original board slots).