First of all, This is not really an issue but it's more a question:
I am a sysadmin for a minecraft players community. We have a long term project and in this project we would like to use quests. But we also would like to use some mods and in a long while we will probably use sponge in order to do that. (Or should we use Forge ?)
Will Quests be continued on Sponge when it will be released ? Will it be possible to have a quests configuration portability ?

I ask this question now to avoid telling later to my players: "Sorry, all the quests you already created will be deleted now we start using sponge to add the custom classes and other mods."

Once again, the project was abandoned by the developer.

Any words on this?

I have no plans to continue development on Sponge. Pull requests are still accepted here and anyone interested in continuing development can PM me on Spigot. Thanks!

It's not even supported on Spigot.Bukkit anymore.

It still work on the last spigot version.

Yes, but it isn't supported.