One of the biggest reasons why SMP failed was because people got bored - the exact same could happen here. If this server is updated often with new features and more to do, I don't think it could die as soon as the other ideas we've tried. We could go as far as changing the gamemode every month - having something new will keep people entertained.
My point also links to the freedom server too. The reason why TF was fun in the past was because we got new stuff every few weeks - such as MoveCraft - and these stayed on the server, with the ones not used much being removed. It didn't need suggestions upon suggestions to be removed. This is something we can see from the past and I personally think we should move in that direction for both the Freedom and SkyBlock servers. I'm sure the development team are working on other things right now, but this cycle of adding new features will help both servers to thrive.
However, the SkyBlock server seems to be in a very rushed state. We can see this in the fact that necessities such as the rules have not been updated to align with our standards. I am also against the server being cracked. With the use of AuthMe, players will be able to log in as others under a cracked client and set passwords. In addition, any players that we gain on cracked clients through this server, we will lose on the Freedom server as they cannot join. Most cracked servers can't go on premium lists as well as there are server lists for cracked servers. Before this server became a part of TF, Premium should've been enabled. The rules should have been set. The server has clearly been rushed to become a part of TF, and it's not in the right state. Any announcements should have come when the server was finally ready.