Bump! Update: 7/28/18Custom Blender ExporterA custom made, python-based exporter is being developed for creating custom bricks (and might support other objects as well, such as items and vehicles). By using the exporter, you'll be able to make bricks or even entire brick packs for Block Party. You'll be able to set up everything needed for bricks within the program itself: The brick model, collision, brick grid, size, vertex colors (including transparency), and even information such as the brick name, category, and subcategory. Once exported, face occlusion will be set up automatically, based on specific textures you use for model faces.
The exporter is not completely finished, but is working, and Block Party already supports custom, third-party bricks. The Blender add-on will be released later on, once finished and once the default bricks are decided on.
Brick Rotation On Any AxisA new feature not quite finished is the ability to rotate bricks on any axis, rather than just vertically. Instead of having 4 rotation variants for bricks, there are now 24; bricks can be rotated using the new building interface that will be developed, or by hitting a single key to toggle the feature and while using the Numpad (very similar to positioning a brick). This feature will expand what's possible with builds.
New Bricks and Building InterfaceWith the new exporter almost finished, there's no limit to what kind or how many bricks can be added. I'm currently working on implementing as many default brick as possible, which range from basic plates, to various types of ramps, new cube variants and various detail models. A new interface for building will also be added, to make creating builds much easier. The interface is inspired by various Lego games, and will allow you to build and choose by using the mouse. You'll no longer have to use the alpha numeric keys for selecting bricks, which was meant to be temporary anyway. =P
What's Next-Print Support
-Building Tool Functionality
-Networking Support
-Reimplementation of Previous Features (since I switched back to PC from the mobile version)
-Shader Overhaul
-Perhaps A Couple Other New Features
-In-Game and Avatar Options (?)
-Main Menu GUI and Map Selection