I've seen the wording, it says makerlights can be used to increase the BS while doing snapshots and overwatch, it's very specific. Keep in mind markerlight hits evaporate at the end of the phase, so for overwatch the markerlights would have to be overwatching, too. (which works with their shared overwatch rules).
Also, drones fire at the BS of the highest BS in the unit, so some maker drones with SHas'O got some BS 5 naturally, baby.
Oh, and there's nothing preventing markerlights from using other marker hits to increase their BS. SO you could use the skyray, which has skyfire and two markerlights, to light up a Flyer. Then you could hit it with a unit of pathfinders hitting it with BS3, to give 4 or 5 marker hits. Then you could shoot a Railgun at it at BS 5, or 5 seekers (which always hit at BS5, defacto skyfire).
I'd have to do some math to figure if that's actually a good use of resources, but yeah, you can totally do that now.