At this time Dimension does not have any modeling or tools for modifying 3D shapes. While modeling and creation is an important part of 3D, it's a very large topic and if we do it, we want to be sure we do it right. We do not have any plans for 2018 to include modeling or creation functionalities.
For this year we are focusing on improving and fleshing out the current features with enhanced materials, decals, support for Illustrator and .svg files, import/export workflows, etc.
The team is currently planning for 2 updates a year (and we're going to have an update any day now). The best place to stay up to date with what features are being actively worked on is our Feature portal! Adobe Dimension CC Feedback Portal You can post new ideas, vote/comment on existing ones, and get a status update for all the things that are added to the planned, started, or completed status.