Although I’ve been a home cook for 40 year, I ain’t never heard about Mississippi Pot Roast until today. Here’s my issue. No one besides me would want pepperoncini in it. What am I missing if I leave them out? Is it pedantry or, because it is so simple, that leaving them out makes it not Mississippi Pot Roast? What if I crock pot it with the pepperoncini but then people don’t eat the peps. Would they still taste the effect and go 
If you are one of those barbarians who just slice it and put it on a plate, it’s probably fine, but if you serve it as a stew in a bowl like God intended, they will taste the peppers.
We’ve made it. Usually it’s a glob of meat and juices. All of which can be flavored how you want.
We don’t do pepperoncini. Personal preference excepted. But there are too many kids eating at my table.
We have a selection of hotsauces available for those who like a more spicy plate full. I like banana pepper raw, with mine.
Sorta like the Chicago/ Italian hot beef sandwich in another thread. There’s just so much you can do with a beef roast. Basically they’re all the same just different spices and how long you cook it. Crockpot will yield a nice big pot of meat for sandwiches. You can pull it if it’s easier to eat like that.
That seems unequivocal. No peps for this crowd.
IME people who say they don’t like peppers or heat positively HATE the slightest hint of it. Their max tolerable dose is zero. Not approximately zero; exactly zero.
You may know more details about your audience that may relax that absolutism.
My own general approach to cooking for heatophobes or spiceophobes is “Just say no”.
Yep. Spice at the table at meals like those. I can’t be trusted to calibrate what “not too spicy” or “just a little spicy” means, because even if I think I’m going a category lower than “not too spicy,” I end up making it too spicy. So I skip it. Pains my heart with Cajun and Creole dishes not to put any cayenne pepper in it, but I’ll put some quality Hungarian paprika instead. It’s still delicious, but needs heat added at the table.
Pepperoncini add their own flavor but can be picked out, my pepper-hating kids didn’t mind but YMMV. I have the fixin’s, might pull elk out of the freezer later.
Bell peppers ok? I’m sure it’s not “authentic” MSPR at that point but it’s probably pretty good. At worst it’s still another pot roast, and those are pretty good.