It's mostly driven by what our customers have asked for. Subtractive processes like CNC have a high barrier to entry (compared to additive), so we started there to make it easier for everyone to get quality parts easily and quickly. Aluminum is a great material that you see a lot in both prototype and final products across industries.
The CAD integrations, materials, and part complexity we support are constantly improving - much more to come in 2017!
Aluminium is already the material of choice for a lot of prototyping and general purpose widget making, and for good reason. It's relatively cheap, easy to machine, lightweight, strong enough, and corrosion resistant.
Automating the design-to-CNC-instructions process is a pretty logical next step.
Perhaps related, any plans for Blender plugin?
Thanks!