The phrase 'when could we' is correct and usable in written English.
You can use it in a variety of contexts to ask a question. For example: "When could we get together to discuss the project?".
When could we say "mission accomplished"?
So when could we expect to see such a device?
Even though a restored Rockaway Beach line may prove acceptable to residents of Central Queens -- which, according to your article, is unlikely -- when could we expect the M.T.A., or whoever, to even begin planning such a move?
If we couldn't do anything after Sandy Hook — Congress chose at that time to reject comprehensive background checks — when could we? If, after the San Bernardino shooting, in December, Congress couldn't agree to restrict gun ownership for people on the terror watch list, how could we enact anything even slightly more ambitious?
One thing that does intrigue me at present is when could we realistically expect to observe any possible subsequent effects of a "quiet" sun?
We next asked when could we first detect the effect of knocking down spib function during primitive myeloid differentiation?
"We have arrested Mladic when we could, when we could reach him, and when we were sure we were following the right trail," he said.
But year after year we returned, always vowing that when we could we'd buy a second home there.
When we could, we escaped the city for vacations in the Dordogne or, as the French say, "Périgord".
When we could we would even run early in the morning before all of the crowds would gather.
We were the better side, when we could play, we played.
