Whenever I submit vehicles for a movie, I wish there was a way for the vehicle comment box to be open only for contributors, so I can place additional pics or thumbnails for a vehicle before they are validated.

True, I could start adding thumbnails soon as an admin validates the vehicle pages and unlocks them, but sometimes they are unlocked as soon as I announce that I am done uploading, or they are not validated until the very next day. I prefer to add thumbnails as the top comment before it gets buried by other user comments and in those instances when the pages are not unlocked until the next day while I am asleep during the night or early in the morning, I find it a little frustrating by the time I wake and log in to begin adding thumbnails and find that most of the vehicle pages already have a pile a comments. It's not so bad if I add the thumbnails under 1 or 2 comments, but under 4-5 or more comments, it looks tacky putting thumbnails under all those comments. I understand that vehicles or movies I submit aren't always validated quickly because of other contributions from other users that are still pending.

That's why, as I mentioned before, I wish there was a feature for the locked vehicles comment boxes to be open for contributors like me, so it would be more convenient to add thumbnails and I won't have to constantly check back and forth from time to time at IMCDb to see if the vehicles have been unlocked yet or not.

Yes it is one of the problems of the current system, as it was a thing quickly done over the current site system.
In the future it is one of the things that will be improved but currently there isn't really a solution.

I had a feeling such a feature was not really possible at this point, but hopefully in the future, as you said, it will be a possibility.

One of my work around with these unvalidated page is I usually write a comment for the subject vehicle with the time index at the movie page. This I work with multiple Crown Firecoach with different fire truck numbers that I placed in the comment page as soon as it validated at the Emergency! TV page.