If you have trustees who don't want to submit fingerprints and photographs, then as mentioned, you have two main options:
1. Create a new trust with a (slightly) different name and list yourself as the only trustee. Get the new stamp approved, then add everyone else.
2. Remove the other trustees from your current trust, get the new stamp approved, then add everyone else back.
As long as there are no other trustees at the time you apply for the stamp and continuing through when the stamp is approved, then you can add trustees later and no additional fingerprints or photographs are required. The only downside to the second option is that your current trustees won't be able to possess the current trust items for the time period that the tax stamp is pending.
I understand the folks who don't see the need for trusts and primarily see them as work-arounds for CLEOs that wouldn't sign. The spousal possession problem is truly mostly theoretical and not a practical issue that people have faced, but it is an actual legal problem that could someday arise. It may not be a reason to get a trust, alone, but a trust does provide some peace of mind on that issue. And, of course, if you don't loan out your NFA items, you won't see the need for a trust either. Personally, I only wish I could afford a machine gun. My best friend and hunting buddy is on my trust, and is able to be in sole possession of my silencers when we're out hunting and are separated. That's a good enough reason for a trust, for me.
There's one other benefit to a trust. Property in your will (you have a will, right? For the love of god, don't die without a will! It's a pain for your heirs!) has to go through a court-guided probate process. Property in a trust goes straight to the beneficiaries without having to get the court involved. I think for NFA firearms, it's easier not to have to explain the intricacies of NFA law to a court. They don't know it or understand it unless they happen to be stamp collectors, and I wouldn't want a valuable machine gun tied up in probate, at the whims of a court that doesn't understand machine guns (or that they're even legal to own).
Just my two cents as to why trusts can have value for some people. Of course, I do sell them to my clients, so I'm obviously biased. But I have one myself, and I think it's useful.
Aaron