"would concur" is correct and usable in written English.
It is used to express agreement with someone else's opinion or decision. For example, "The committee discussed the proposal and I would concur with the idea."
Most independent observers would concur.
Developers and agents would concur, it seems.
"Hopefully we don't destroy ourselves first," Josh would concur.
Judging from "Asylum," his muse Ms. Kawakubo would concur.
Few policemen or prosecutors would concur; most believe that the Calabrian version is even more dangerous.
It is unlikely Appleton would concur that the two managers are working in similar circumstances.
The Japanese, Vietnamese and Indians, among others, would concur that these still have a long way to run.
Anyone studying his CV would concur and might also believe he has enjoyed something of a gilded life.
But she doesn't think she was wholly unpopular – and the elder sister of a schoolfriend of mine would concur.
(I would concur, if not for a certain colossus called "Porgy and Bess" and a brash upstart known as "Nixon in China").
