Online trends, like their offline counterparts, are cyclical. As an example, today's teenagers wear similar styles to those popular when I was that age.
Yeah, we had Vans also. We had Converse. We had Nike.
We invented electronic music. Or did we?
When a trend happens, there is always a backlash. So if you're worried about the topic of your podcast, or even podcasting itself, not being trendy, don't.
If your topic, platform, or other preference isn't currently popular, it will be eventually. So instead of chasing trends, delve deeper into what you love and stay ready for its eventual resurgence.