I'm trying to find some numbers / data / studies / testing that uncovers the maximum number of scrolls (swipes) that should be used on a mobile site in determining page length. I know the typical best practice is to keep content short and sweet for mobile, but longer pages are ok if it's engaging and relevant. We are currently using truncation rules for longer pages and headers to break up the content, but I can't seem to find any stats or research around page lengths for mobile.
There is no magic number of pages / swipes. Ideally, the length of content should be as short and as simple as you can make it without negatively impacting the content too much. Incidentally, the same rule should apply to all websites, and not just mobile. This is always going to be a balancing act and will depend on the type of content and audience.
For example, if your site was focused on short stories or novellas, it would be reasonable to have content 20,000 words long as for that purpose, it is appropriate. However, if you were listing sports results, 200 words may be too long.
Take Wikipedia for example. If you were to check out the World War II page formatted for mobile use, you will see that it is long. Is that too long? No. It's the right length given the content and the intended audience.
TL;DR: Optimal length depends on content and audience
There are websites with no scrolling on mobile and there are websites with infinite scrolling. It depends on your content and your ability to hold the users attention. If you have sections, use a good navigation to let the user jump to a section rather than having to scroll through the entire list. In this scenario, the user know what they want and the other information may act as a hurdle.
In social platforms, people get away with unlimited scrolling since the content is something which is a surprise, people are willing to spend time on it, and there's always a search if you don't want to 'waste' your time.
With that said, I will makeup a nice one liner: Let the content decide the length and the intent decide the navigation.