Yeah, completely unrestricted use.
However, with the experiments in twin zones, I can see Singapore having room for three.
One of the big challenges of the DRS allocations is that the FIA needs to allow for space for the detection software to work. That’s why Montreal didn’t have separate DRS zones, one on the back straight and one on the pit straight. There wasn’t enough space. However, Singapore would allow this, with three zones:
1) The first would be on the long back straight, along Raffles Boulevard. The detection point would probably go somewhere in between turns four and five.
2) The second would fit along the Esplanade Bridge, the long straight after the Singapore Sling. The detection point would probably be somewhere either side of the Sling itself, probably after it.
3) The third and final DRS zone would go on the main straight, with the detection point somwhere in the waterfront section, probably on the straight behind the grandstand or before the final corner.