System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce MX130/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 456.38

Blender Version
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-18 16:11, hash: rB7b988188dc3f
Worked: 2.90

Short description of error
As the title states, Import Images As Planes Imports Alpha as Emission Strength (new Principled BSDF value recently added in D4971)

Exact steps for others to reproduce the error
Based on the default startup

1. Go to Preference Settings and enable the "Import Image As Plane" addon that comes with Blender
2. File > Import > Images As Planes, and choose any image that has an Alpha channel
3. Go to the Shader Editor, and see how the Alpha channel connects to the new Emission Strength of Principled BSDF