Do not underestimate client-side verification. Privacy also much harder with trusted WoT services.
WoT Providers should be optional and ancillary to client-side processing of events.
Also, do you think WoT is not portable when it is calculated client-side?
It is open-source code we are talking about. Anyone can use the same algo.
So:
1. Depends on requirements. Global is much faster and cheaper, but less about you. Should be left to the user. #Vertex does exactly this
2. Standardization I welcome. But there are trade-offs to third-party WoT see on top
3. Yes, user choice is welcome to the degree a non-technical user is NOT left to his own devices by default
4. Agree - privacy is most achievable with client-side calculations or self-hosted services which will be very niche