Well in the old days, the operating system was there to help you. If plugins were standalone processes, they could be resource-constrained. But they all have to run in-process because of the LAMP architecture.
Thanks for the article, it's insightful and I & history agree completely with you. Nowadays, people are using prebuilt VPS images or automation scripts to provision their servers and shared hostings are becoming more of a VPS hostings with a good UI around these tools.
I see that you are a WordPress veteran, nice to hear your opinions :)
I see that you are a WordPress veteran, nice to hear your opinions :)