its definitely possible today. i don't think it is unreasonably difficult either. however, if you are looking to get to d1 as soon as possible from the start of the world, going to d2 is usually the best bet. but for a long time d3 coach, jumping to d1 i believe can be achieved with a couple really good seasons. if you are make the S16 4 times with a final 4 or couple elite 8s, you are probably safe - especially if you have all high win seasons. i am sure you can get into the C range, but that does take a fantastic run, so getting into the D range is definitely a reasonable goal - don't expect it to be easy though!