Its easily possible to go below 10kg with the Birdy.
Its frame isn't heavy, the solution is to suppress some accessories like mudguards, easy wheels, folding pedals (fixed pedals can weight much less) and use lightweight components. Its what is partly done n the Pacific Cycles Birdy R20 11SP which is a 20"folding bike and according to Pacific Cycles weight 10.2kg with several components that can be replaced by less heavy ones.
The Brompton T-line is under 8kg and can also have its weight reduced by changing some components.