Newest update...

Previously, I had inquired Delta as to the validity of this whole issue and got a response here.

I have since replied that it's not really an option to "pull items from my bag and carry them on" since the whole point of the carry on bag is that I'm carrying expensive camera gear or laptops and the bag is for their protection/organization.

Here is their latest response:
I do understand your concern with the way the agents are handling the carry-on bag policy - especially since the last situation involved a Red Coat. I get your frustration in being told you have to gate check your bag, when you have special items in the carry-on bag that you didn't want to be put in a checked bag. We realize that more passengers are taking carry-on bags, so there has been an increase of bags checked at the gate. Both our gate agents and flight attendants, should be monitoring and in constant communication during the boarding process; to ensure that passengers are only bringing one carry-on bag, and that all the bins have been filled. So, if this isn't happening we want to know so we can address it with the appropriate team members and leadership team.

One suggestion I can give both you and your wife, is to bring a small personal bag (which is allowed) so you can move items into in case you do have to gate check your bag. I realize this isn't the ideal situation, but it's something that I do and is a quick solution to keeping some of your personal items with you. As we continue to review our carry-on bag policy and procedure, your comments will help us improve our service.

So now we enter into a new realm of definition...between "carry on bag" vs "small personal bag (which is allowed)"

Again, my response was non conclusive when asking:
in the mean time, before the leadership teams come up with a process that is known to gate agents and customers alike, when I have to tell a gate agent or flight attendant that: "No, I will not be checking this bag because of the contents - it will fit under the seat in front of me" - what option do I have?
other than coming up with a "small personal bag" ???

I think I'll come up with Cabin OK sized bag that fits in a normal sized carry on roller bag. Then when I say, can I remove the contents and carry them on - I'll just unzip the larger roller, pulling out a smaller roller.