One way would be to share the article with them and explain that replies directly in a channel make it harder for you to catch up. Saying that threads make it easier and quicker for you to decide what to read.
I usually start by proposing an idea to a small group of people - e.g. my team or people at the company I think might like the idea. Only after a few people say they like the idea and start using threads, propose the idea to more people and say "look, a few of us are using threads and it works".