The main reason for the delay of the alpha release is the 1.14 update. Unfortunately, 1.14 could be seen as an alpha release for Minecraft itself - the new features gifted by Mojang are great for servers like us, yet have caused widespread catastrophic performance issues.
Due to this, development of IslandEarth has slowed. A large majority of important plugins - such as Citizens, which we use - have a large variety of bugs or have simply not updated yet as a cause of the major changes.
Development will continue, but at a slowed rate. 1.15 will be particularly interesting with the new combat, and potentially custom NBT for mobs. Even custom blocks are possible now! In any case, let us look to the future. The end of 2019 and beginning of 2020 will be an exciting time.