Some will say that there are set "subscriber thresholds" regardless of your channel's content, but it's not as clear cut as it seems. It is heavily content-dependent. If your content doesn't appeal to a general audience, you'll see steady growth throughout your entire YouTube lifetime based on people's perception of your content's quality with "explosive" events occurring either from an external source, or a video that was featured/suggested and garnered a good response from a broader audience.
Expecting your channel to finally "snowball" based on hitting a certain amount of subscribers is wishful thinking. Just look at sub rates on different popular channels across different genres and sub-genres. They all not only gain subscribers at different rates, but some "snowball" or "explode" at different points.
Personally, I saw steady growth from 0 to 50,000 subscribers with a steady increase in subscribers per day, capping off at around 250 subs a day excluding days that I was featured in online articles. It wasn't until my content was picked up by YouTube itself through features/suggestions that I broke through the 250 threshold, with my sub rate now sitting at roughly 1k per day.
You're best to project the growth rate of your channel based on growth trends you already see within your channel.