The McLaren ace warned it sounded like "a recipe for disaster" to have the sport's new-look "low downforce" cars, still untested in race conditions, jostling for position, and he also brought up uncertainties surrounding overtaking.
Piastri noted his concerns after a successful but very long day behind the wheel of his new McLaren on Friday in which he churned out 161 laps - more than anyone - and finished fourth quickest in the standings behind a Mercedes 1-2 led by Kimi Antonelli.
Piastri believes his concerns will need to be looked at before his home grand prix in Melbourne in three weeks when the first race will take place since F1's cars, rules and regulations were completely revised.
"Starts need to be addressed, because, probably as we've all seen, it's a pretty complicated process now to have a safe start, let alone a competitive one," he said after the final session of the first official pre-season testing at the Sakhir circuit.
"There's plenty of topics to address. Starts, and overtaking is certainly going to be different as well.
"Whether we use straight mode at the start or not, as well.
"I think a pack of 22 cars with a couple hundred points less downforce sounds like a recipe for disaster to me, but there's a few of those aspects that need to be spoken about.
"The thing is, everyone's going to need different things for the start, and to be completely honest with you, I'm not sure any of us know exactly what we need yet.
"There's so many things just from an even borderline safety point of view that need to be kind of figured out on track, that do need addressing."
Piastri was talking to reporters after the drivers went through a practice start in Bahrain, which turned into a fairly chaotic exercise, but he said that wasn't connected to the new engines but to a miscommunication.
The Australian had failed to get away in his McLaren but explained: "I got told to wait until whoever was in front of me had gone and then do my own launch, and not do it to the lights.
"Clearly, some other people had a different idea. So that was nothing to do with the power units."
As for his verdict on which teams looked most powerful over the week - McLaren, Mercedes, Red Bull and Ferrari all seemed their usual powerhouse selves - he shrugged: "Where we are in the pecking order, I don't know.
"It kind of looks like the top-four teams are still the top-four teams, but I don't know where exactly we sit in that at the moment."
Mercedes' George Russell, second quickest on Friday ahead of Ferrari's third fastest Lewis Hamilton, was still adamant Red Bull had a "pretty scary" advantage over the rest as Max Verstappen finished fifth on the timesheets.
Red Bull, in turn, reckoned Mercedes looked impressive as the pre-Melbourne mind games started to get into gear.
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