I have a decent frame for my short height of 65.5 inches. I don't workout actively at all and my bideltoid width is 21.25 inches when flexed. This is with large rib cage and decent sized clavicles bones. I'm neither skinny nor fat or buffed, although I have some muscles from occasional workouts, but nothing special and certainly not even close to natty limit of what could be achieved with my body.
When I edit my full-frame photos and add about 2.5-3 cm per deltoid area, I look great to be honest. That's due to my above average head size. If I had an average or small head, my current bideltoid width would be enough to look insanely broad shouldered in photos, but since shrinking the head is not possible, only way to improve the shoulders-to-head ratio is to become more wider.
Another issue is that my neck is thin so it amplifies the disproportion between head and neck / frame. I need about 18 inches of neck circumference (currently at 16 inches) or about 14 cm width to not have a lollipop effect with narrow neck and wide head. This is achievable with a neck harness and resistance bands (already gained an inch and a half of neck circumference in about a month of training every day) in about 3-6 months of timeframe.
But, since I need about an inch of bideltoid width per shoulder side (so 2 inches in total to clear 23.25 inches) to look great, I'm doubtful if I can achieve it with natty training. A full inch of total width gain is realistic in a couple of months with vigorous training of shoulders, lats and back muscles but I don't think that I can gain more than that amount in a reasonable timeframe unless I roid.
That's why 1 inch lengthening per clavicle is significant width gain since it's a permanent solution. Another inch with natty training and total of 3 inches of bideltoid width gain is insane difference in one's frame.
But, since I never worked out seriously in a gym and never took any supplement like protein powders, creatine, etc., it's too early to speculate what my genetic potential is for frame width gain with muscles. So, at least a year of rigorous training and decent diet with all the supplements for muscle growth is what I should aim for in the first place to see how much width can I get.
If I won't be satisfied with the results, I might go and do that shiet for about 2.5 cm per side (upper safe limit). More than that is impossible without severe consequences and diminishing width gains (i.e. above an inch of clavicular lengthening is no longer a 1:1 translation of lengthening and width gain).