It would be like all players can simply set out an nether frame made out of glowstone and then put out water in the frame like you do with nether portal but with water. It would be an Aether portal but not to the Aether, instead is goes to skylands.
Use MultiVerse. You can create portals out of any material you like and link them to any other portal or world. This isn't quite what you want, as only admins can create the portals, but it's something.
http://forums.bukkit.org/threads/tp-misc-pinapp-v2-a-revolution-in-multiworld-1060.31882/ This is a WIP but it'll be done soon. You can have any material as the frame and it lets you light the portal just like you would a notch portal! It's not quite what you're looking for but it's closer than multiverse, as anyone with permission to can create the portal.
