An addon for Botania that lets me upgrade the elven portal with three tiers: 1 lets you send passive mobs through the portal, getting different passive mobs back (and just dissapearing hostile mobs), the second one lets you get stuff/new mobs from hostile mobs, and the third and final upgrade lets you yourself finally go in and explore the elven realm itself.
Obviously increasing mana costs for the portals as you upgrade it, plus the materials for the new upgraded portals are rare/expensive/hard to get; but with each new upgrade, you also unlock new item trades too.
And/or extra realms/portals. Like a portal to the dwarven realm under the bedrock but above the nether, which at first works similar to the elven portal but with living stone instead of living wood. If both ideas are used, the dwarven portal could be upgraded too, ultimately resulting in you being able to explore it. And if there's 2 portals now, why not 4? Make a Cursed Daisy, which has all the same recipes as a pure daisy, but which result in cursed or evil versions of the things you would have purified, get bleeding wood and make a Drow Portal, or get Death Stone and get a Necropolis Portal, which also can be upgraded. The items you get from the new portals can be crafted etc in order to make new weapons/armors with slightly different benefits, and to summon new bosses.
So with these ideas, the Tier 1 upgrade only requires materials from the original portals, probably not all of them, like the elven upgrade requires materials traded from the dwarven portal, the dwarven upgrade needs materials from the necropolis portal, the necropolis upgrade needs drow portal materials, etc. Tier 2 upgrades require materials from Gaia spirits and Tier 1 portal passive mob products from the same portals, which means you need to make a third portal to make the second one tier 1. Tier 3 upgrades require tier 2 hostile mob drops and drops from some of the new bosses, which if they only need drops from the one other portal, now you need all four portals anyways (though to make only one portal Tier 3, one portal only needs to be the un-upgraded version, one is tier 1 upgraded, and the last one is teir 2).