From what I've read, downloading a full Daedalus node is currently around 6-10GB. Do old UTXO's ever get pruned from the blockchain? If not, what's to stop the size of the blockchain from growing indefinitely to the point where it's impractical to store on consumer hardware?
No, it never gets pruned. One of the appealing features of blockchain is that the history stays there forever.
The size of the blockchain grows roughly linearly (ignoring the effect of adoption), whereas storage capacities follow Moore's Law and grow exponentially. So the expectation is that, yes, the blockchain will grow bigger and bigger, but that that is no problem, because hard drives get bigger (and cheaper) faster.
For the second part of your question (what's to stop the size of the blockchain from growing indefinitely to the point where it's impractical to store on consumer hardware?), there are concepts like sharding and side chains and .... You can watch Charles Hoskinson talking about this topic here.