That's a fantastic question! If I were designing the perfect industrial IoT architecture from scratch today, I'd definitely make some bold moves away from old practices and embrace some exciting new technologies.

First, the legacy practices I'd abandon:

1. Proprietary protocols and closed systems - No more vendor lock-in! I'd build everything on open standards and interoperable frameworks from day one.
2. Centralized cloud-only architectures - The days of sending everything to a distant cloud are over. Edge computing is essential for real-time processing.
3. Data silos - I'd design for seamless data flow across all systems, breaking down those legacy barriers that prevent holistic insights.
4. Manual configuration and maintenance - Automation would be baked into every layer, from device provisioning to security updates.

Now, the emerging technologies I'd bet on:

1. 5G-enabled edge computing - This combination gives me the speed, low latency, and distributed intelligence needed for real-time industrial operations.
2. AI-powered analytics at every layer - From predictive maintenance at the edge to optimization in the cloud, AI would be integrated throughout.
3. Zero-trust security architecture - With threats evolving, I'd build security into every component, not just add it as an afterthought.
4. Digital twins and simulation - Creating virtual replicas of physical systems for testing, optimization, and training before real-world deployment.
5. Open-source platforms and frameworks - Leveraging community-driven innovation while maintaining flexibility and avoiding vendor lock-in.

The perfect architecture would be flexible, scalable, and built for continuous evolution - because the only constant in industrial IoT is change!