No comma with a non-defining relative clause

Swiss International Air Lines is now part-way through its multi-million dollar 'Next-Generation Airline of Switzerland' strategy which, this year, will see the introduction of two new aircraft types and numerous product enhancements. (Airliner World, June 2016)

In the above sentence, no comma is used before which even though it begins a non-defining relative clause. No doubt this is because the time phrase this year has been set off with commas, and a third comma before which wouldn't look very good. If we place this year at the end, a comma seems necessary: Swiss International Air Lines is now part-way through its multi-million dollar 'Next-Generation Airline of Switzerland' strategy, which will see the introduction of two new aircraft types and numerous product enhancements this year.

This is an example of how impossible it is to give hard and fast rules about English grammar. It also proves that everything must look good to pass for natural English, however incorrect it may be grammatically.

CB