There's no real reason for the UEF to actually pursue Q-ships. They don't have the resources or time to implement that. If Steele can attack in anything less than months, then it's a waste of time/resources. If they had any to spare, they'd be repairing/building true warships. Q-ships make more sense against stuff like pirates or the Gefs (maybe, since even they have military surplus essentially).
Also given the fact that if you can send a cruiser from Earth orbit to the convoy in 30 seconds no matter where they are (I didn't realize subspace was like that before), you don't need a Q-ship. You can just listen in on the comms and when you get a signal, you send your defence force. It actually makes you more flexible with fewer assets.
Another thing, the Tevs have a technological advantage here. They have better offensive weapons (read: beams). The only way UEF forces really can press an advantage is by keeping the range open beyond 4 km. And that's with capital-class railguns/mass drivers. Q-ships don't offer any real benefit in that environment either. Unless you armor your ships like a frigate, it's useless, and once you get that much metal on a frame you might as well build a warship.
Really, the nature of subspace kills the idea. It doesn't really cost you to hold your forces in reserve because it doesn't cost much to deploy anywhere. Besides, we need missions to fly, and this gives us exactly that! Jump five shifts, here we come.