"It’s been said before and bears repeating, “the days of low-priced plugins and unlimited everything are going by the way side.” WordPress product businesses that operate with unlimited anything are almost certain to fail as it’s an unsustainable model. Customers need to realize this sooner rather than later."

Actually, it gets no truer when it's repeated than it was the first time someone said this. Since when has there only been one way to compete in a marketplace?

Each plugin developer needs to work out for him- or herself how s/he plans to compete and be successful (including financially successful). Sometimes the apropriate model will involve charging recurring fees and providing long-term support. But by no means always: providing support can be very expensive, and it can also be difficult to ensure consistency and accuracy among support staff. Lack of consistency and accuracy can undermine the brand so badly that the whole thing unravels.

There is another way to compete, which you seem to have overlooked. That is simply to sell more units. (Interestingly enough, the world's biggest corporation essentially follows this model.) Unless the market in WordPress plugins is already saturated, which it clearly is not, this will also continue to be a perfectly viable business strategy for some.

I don't think either of us in a position to tell each plugin developer which model will suit them best. All we can say for sure is that it is a question they need to consider and make an informed decision on.