My grandfather didn't walk until he was over 2 years old and I walked late (another bottom shuffler - I think anything up to 2 years old is considered acceptable in the bottom shuffling community...). Nothing wrong with either of us, we were just late walking. My eldest son, however, was late walking because he has low muscle tone (hypotonia) and hypermobility (loose joints). He did need orthopaedic boots (piedro boots) for a while to help support his ankles when he was learning to walk (and also had physiotherapy, as at 15 months he couldn't even roll over, let alone bottom shuffle, crawl, get from lying to sitting or sitting to standing). He is now 4 and can run, jump and even hop. He did need a lot of encouragement, though, as he had to build up a lot of muscle strength to counteract the effects of the hypotonia and hypermobility (still haven't had all the checks to ensure this isn't down to a connective tissue disorder, but he seems otherwise pretty fit and healthy, and well co-ordinated).
So, I know how you feel. Not much advice, though, except to try and get him up and cruising/walking with a cart as much as possible (my ds would spend lots of time ploughing up and down with his cart, which looked a bit odd by the time he was able to do it as they're designed for 12-18 month olds, and he was an extremely tall 20 month old when he first started being able to push it along - and just under 23 months when he started walking independently).
Have they made any comments about your son's muscle tone or that he is or may be hypermobile? These are fairly common causes of late walking, I think. Has he had any physiotherapy? This might help if his late walking is caused by anything other than his temperament and own internal learning-to-walk timetable (as I said, it's fairly unusual, but not necessarily considered abnormal for a bottom shuffler not to walk until they are 2).