Like I said, I don't like Wordpress either. But within the constraints of shared hosting LAMP, guaranteed isolated processes are not possible. PHP adds a lot of introspection, so anything declared anywhere can be read or changed.

Wordpress is not alone in this. It's the platform.

You don't need isolated processes to have better architecture and a sane plugin model.

We're still talking about different things. Yes, WP could be better. This is demonstrable from other, better-designed engines within the LAMP/shared constraints.

But no such system can prevent any plugins from doing whatever they want to do.

Introspection & Reflection in PHP don't expose everything, and frankly even if they did, it would be quite easy to analyse plugins and have an approved list of "safe" plugins that is used either as an advisory or as a basis for the available plugins shown to a user.