Thing is, a lot of the old "cardboard" vacs were basically a plasticised or varnished paper, so it was an early form of plastic construction, rather than being something that looks more like the inside of a toilet roll coated in paint...
Plus, making cardboard vacuums in the sense of the Vax one, it's not really green in an ecological sense, as if it's designed to be thrown out, then it's going against what people are trying to avoid, unnecessary waste, financially and of natural resources. Cos when you think about it, where does most of the paper that makes the cardboard come from? Trees, and I doubt that there'll be any justification to plant forests of trees just to supply the world with disposable vacuums...
And the fire part, well, you cannot make card or paper fire *proof* without making is unusable, just fire *retardant*, meaning it contains chemicals that produce CO2 gas to extinguish flames if it gets hot enough, but if the heat is intense enough, even fire retardants can be overwhelmed...
It's an intriguing project for a student, but to me, that's all it is and will be, it's not a sustainable product, and doubtful that it will make it to market, and even if it does it won't last long...