tl;dr, podcasts are expensive to produce, about $1000/hour with video, hosts (local and remote), and post-production. TWiT is going through hard times and some shows and hosts have to go. Sadly, FLOSS was on the chopping block.
Advertisers just aren’t interested in podcasts anymore. If you still want to support the network after this, give Leo $7/month and join Club TWiT. I don’t give a rat’s ass about Discord, but I do want to prevent stuff like this.
Apple tried it a decade ago. It was called the Fusion Drive. It performed about as well as you’d expect. macOS saw the combined storage, but the hardware and OS managed the pair as a single unit.
If there’s a good tiered storage daemon on your OS of choice, go for it!