“It feels like we’ve been working on this for a year now, with more than half a million lines of code changed over 1,104 commits we’ve been working extremely hard on this update,” stated Mojang via a post on its website.
Version 1.7 is set to include lots of code changes pertaining to the plugin API in addition to more than twice the amount of ingame biomes.
Such changes included in 1.7 include things like new world generation, new block, enhancements to fishing, enhancements to maps, an overhaul to achievements and stats, more multiplayer features, chat and command improvements and tweaks to resource packs.
Meanwhile, the developer is asking for help testing the pre-release. You can find further instructions along with release notes here (Mojang.com).