This page links to an in-depth paper titled "Overcoming Roadblocks to Industry 4.0" written by Parks Associates (an IoT Research and Consulting firm) and Nokia. According to their findings, the top 5 roadblocks are:

1. Networking capabilities and the operating environment
2. Data architectures and infrastructure
3. Cybersecurity and cyber threats
4. People and processes
5. Working with vendors

It's an interesting read (and a free download) to help companies realize their full potential in the digital world.