So I can make 1000 free accounts and get anything I want on trending? Well at least until someone makes 1001 free accounts. There is a reason why RC's exist as most abuse fighting tactics are easily avoided by making a new account.
This is a problem that has always existed on the internet. Not having it consume RC's is just an idea and we could also make so that it consumes some. The details so to speak are up to debate.
The other issue, is people with no stake would have equal share to decide what goes on trending. That doesn't seem fair to those who paid thousands and hundreds of thousands to have a large amount of stake, or those who don't sell Hive as fast as they make it
This is where the idea of having both systems overlapping would come in: "upvoting" and therefore stake still matters and we could experiment by starting with a distribution of 75% "upvoting" strength and 25% "like" strength (again, the details are up for debate). But as I pointed out PoB doesn't work currently. Likes could in a sense mitigate this problem
Check out https://www.steemfiles.com/hive-102930/@tobetada/introducing-a-like-button-to-hive .
There is KYC everyone or use money to prevent sybil attacks.
There are certain changes a front-end maker can do, and certain changes that a front-end maker cannot do. We cannot change the way the blockchain rewards content. The trending page is something that is on the blockchain consensus so this is the same everywhere but a front-end could have a parallel kind of system that uses only what its users does and not the blockchain (for likes). This way your like on one site wouldn't be available through the full-nodes to another but they could conceivably be made available through a public API or perhaps even another blockchain.