This morning, the Luxembourg VAT administration confirmed that you can postpone the VAT payment provided you introduce a written request through MyGuichet (and provided you have cash flow issues due to the crisis).
As the filing deadlines are extended, I recommend to draft the VAT returns and to validate them later. You avoid thus a VAT payable position (and you don't have to ask for this postponement).
Should you have any question, please call me 6126.96.36.199.
Take care ! Isabelle