Is that a Warmoth body?
I have 4 open bodies here right now. Two are rear-route VIPs, and two are top-route Strats. The VIPs are routed for humbuckers, and you couldn't put single coils in the VIPs even if you wanted to because there's no pickguard to hide the hole(s), but if you could, the holes wouldn't be wide enough. On the Strats, one was routed H-S-S and the H hole is ~2 7/8" wide vs. the S holes which are ~3 1/2" wide. The other was routed S-S-S, and I re-routed it to take a humbucker, which left some space. Out of curiosity, I went and grabbed a single coil pickup and tried to fit it into a humbucker route, and it it wouldn't go. I've got another Strat that's already assembled where it was routed H-S-H and I had to route the neck H hole to fit the S.
So, that's what I'm basing my answer on.
Warmoth may be routing their humbucker cavities differently now from when these were cut, and judging by the picture you show, that seems to be the case. Unless that's not a Warmoth body, which is why I asked. It would be possible to route the way yours is and use single coils without compromising the ability to use humbuckers, so that's the way they should do it. But, it would rely on a pickguard to hide your decision.