It's worth noting that in the mid-eighties, transwarp was a success as far as anyone else knew. According to the Enterprise-A bridge graphics in Star Trek IV (Mike Okuda's first Trek contribution, I believe), the ship was packing transwarp drive too. FASA was knocking about around that time, was it not? I never heard of it until recently.
TNG made things a bit clearer, and "transwarp" was always a super-advanced tech associated with the Borg. With the exception of the newt episode... I think Praetor's done a great job of retconning everything to make sense.