While I agree with HD that "monitor" on transfer from radar to tower is a very bad idea, I have never seen a problem with it for the queue of aircraft awaiting departure. I sometimes wonder what part of "monitor" pilots don't understand, when there are 10 aircraft ahead of them, a steady stream of inbounds and someone over the fence awaiting landing cearance, which comes even later because you want to put your towel down. And given the scenario above, I would be astounded if you were not ready when your turn came. While you are waiting, I should think you establish that you are actually monitoring the correct frequency, so it is rare that a monitoring aircraft in the queue is not listening when his turn comes.
If traffic levels are low and you are taxiing towards the hold with nobody else there, then by all means tell us that you are ready (and that you could depart from intersection xxx), but we are likely to be ahead of you there and to have asked you to report ready if we are going to be able to make use of you. We want to make most use of the runway (delays are hard work), so believe me you will be airborne as soon as we can possibly get you there.
As for squawking ident on the ground to signify ready - nice idea, but I'm not sure it would be of benefit - If ASMGCS (ground radar) was able to show your ident it only shows for seconds, so I don't even think the departure controller would even necessarily notice, when they are looking out from the visual control room. Notwithstanding BAs difficulties, we would normally expect you to be ready at the hold when you are number one and if experience tells us that you may not be ready we would ask you to report when you are. [/Ramble]