I can't access the ABC article. For some reason the website won't load. Without trying to sound ignorant and arrogant, surely we'd know if people were experiencing toxic levels by now? It's been multiple decades since energy drinks became a mainstay in society. I know plenty of people who drink multiple daily, sugar, and sugar free.
I'm yet to meet a single person who's experienced any issues related to b6 toxicity. I do know people who've had to cut back their intake due to consuming too much sugar though.
I personally refuse to have the sugar free variants. The majority of them use Sucralose as their sugar replacement and that destroys my guts more than normal sugar. Studies also state it may destroy healthy gut bacteria too. It's in far too many products, and I'll take the full sugar version of the alternative every time.