As someone who has used Autocad since Ver 9 (1993) this is important.
Also - heavy 3D design. Blender/Alias/whatever these days.
Solidworks as well.
Edit: I presumed that the context of the discussion was apps in a general sense. Obviously not every application is going to be on the web and there are a lot of niche software that will never make the switch. I was thinking more qucad or sketch 3d for woodworkers to plan their desks, not solidworks and all its plugins to handle complex fluid simulation in mission critical areas.
1. Pricing model: For the simulation side of EDA, you need a lot of computing power. With desktop apps, the user already has a powerful machine available that you don't have to pay to use. With the cloud, you need to pay for all the machines so finding a pricing model that works is a challenge.
2. User expectations: The users who are willing to pay > $100k/seat/year expect very advanced features that would probably take 10s or 100s of engineering years to get working. These users also don't care as much about the UI/UX problems that a modern app would solve.
References
The BIM stuff (i.e. Revit) is very Windows-specific so a straight port with WASM is a no-starter.
The actual 3D rendering with WebGL is the least problem, we have that nearly solved (in terms of performance relative to desktop -- we never really needed 60fps anyway). The problem there comes in when you have a huge design that does not fit in the allocated/allowed heap space.
(throwaway for obvious reasons)