It's viable indeed, tho you'll need large amount's to get enough profit for a viable income. Atom for instance has 10% APY which is relatively stable, tho some variation in it's price, currently $27. So if you put $100 000 into Atom now, you'll get $10 000 per year, that's $833/month, so maybe just enough to cover your basic costs.
If the price goes up to $50, you'll make $1 600/month, if it goes down to $10 you'll make $300/month. It's a bit of gambling I guess but not too much worse than running a business. After all it's passive income and any passive income is good right. It's free money. 👌