ETIAS was basically approved in April 2016, after much very public discussion and some controversy -- a few months before the UK's Referendum on Leaving the EU in late June 2016. If someone told you it wasn't going to happen, or wouldn't impact UK citizens, they were not credible in saying that. Leaving the Single Market (not leaving the EU) sealed the UK's fate with this, but it's nothing specific for UK citizens, but a blanket rule for people who are not citizens of EU or EEA countries or Switzerland or some of the European microstates who are considered de facto Schengen.
I question that this was "the UK's idea", though, given that it only automatically applies to the Schengen zone, and the UK has never been part of or seriously considered being part of the zone.
This won't impact UK citizens travelling to Ireland, as it's part of the CTA, but I would not be surprised if non-Schengen EU countries like Bulgaria, Croatia, and Romania adopt a parallel scheme, and possibly also EU candidate countries.