> I think considering the Standard Model a moving target is still reasonable
IMO no. The standard model isn't just a table full of particles, it's much more. One core part is is the description of how these particles behave, and the lagrangian. These could change much more drastically if a new particle turned up. This is because the particles in the standard model are intimately tied with underlying representation groups, which can't accomodate another particle. It's possible folks would still call it the "Standard Model", but I suspect such a drastic change would get a new name.
IMO no. The standard model isn't just a table full of particles, it's much more. One core part is is the description of how these particles behave, and the lagrangian. These could change much more drastically if a new particle turned up. This is because the particles in the standard model are intimately tied with underlying representation groups, which can't accomodate another particle. It's possible folks would still call it the "Standard Model", but I suspect such a drastic change would get a new name.