I think you've got the context of this thread mixed up a bit, let me clear some things up.
There are definitely players who have way too much time on their hands and will troll specific players for hours. I've been a victim of that. I've had cheaters follow me everywhere to the point where I need to log off for an hour to wait it out. Even if I'm nicked, they can still check the minecraft menu to see where I'm in the game.
Correct, but judging from my past experiences with FFA cheaters, they would definitely choose to go after good players for more attention, rather than randoms who won't. The only exception is if they are using InfiniteAura (long-range killaura) to get massive killstreaks. But that already happens today.
FFA lobbies fill up like that. In an average full 40 player FFA lobby, about 90% of the players are normal minecraft players wanting to play for fun, and 10% of it being well-known players. Cheaters will always go for the better known players, unless they're allied with them. That's something you'll pick up on once you play FFA long enough. If VIP servers are implemented, nothing about the playercount is going to change, just the normal servers will be filled with more normal players, and the VIP servers will be filled with well-known, better players. Cheaters will still be able to join the normal server, but they won't get the thrill of trolling good players.
If I were a normal FFA player just trying to have fun, I'd be rather happy if all of the sweats were gone.
Like I just said, without the sweats, killstreaks would actually be much easier. You might attract the attention of a cheater once your killstreak gets past 30, but that's no difference than how it is now.
If you have them added on your friends list that's an entirely different story. And no, they don't need to have you added in order to follow you. It's basic stream sniping techniques.
Again, 50% of the map is not going to be gone, and hackers are not going to have a bigger chance of killing you. The playercount isn't going to drop or change; the maps will be full as usual. Killstreaks should be the same, if not easier than before. My guess is you may need to join private servers if you want to sumo good players, but I'm sure there will be plenty of normal players who have the iq to know what sumo is in the normal lobbies.