Knew it was coming, ETOPS will affect all aircraft despite the twin in the abbreviation
One needs to look at the history.
Pre-ETOPS, the design/operating standards required that multi-engine aircraft be able to meet certain performance standards with two failed engines else they were restricted by the 90 minute rule.
Clearly this affected all twins but, also, restricted some 3/4 engined machines.
As the reliability of engines improved, we saw the introduction of (progressively longer) ETOPS operations by the larger twins.
As engine and systems reliability has improved over the years, the concern, for some years, has been less with the (number of) engines and more with other systems considerations - ergo, the number of engines is now largely irrelevant, with the concern being more along the lines of "if we are a LONG, LONG way from a safe haven, how are we placed if this, that, or the other circumstance might occur ?"
It might be better to replace ETOPS with something like "operations remote from suitable aerodromes" and move away from a concern specifically directed towards the number of engines.