Create a full blown Visio app for iOS, a viewer is better than nothing but not by much
Joseph Bratton commented
Make this compatible with the iPencil also to allow for comments, quick edits, etc.
Our department uses Visio on a daily basis, and the field techs use iPads for remote accessibility. It is becoming more of a time saving tool to have them correct drawings while still on-site, other than just viewing. Having a full blown app would be a benefit to not just our company, but to the many companies who enjoy using the VISIO software to maintain proper documentation.