I think a good idea was to have a universal word count over several projects.
Sometimes I have two or three projects opened at a time. I random mind over my word count, adding to this project or another, but the word count does not follow my efforts.
Is this feasible?
Do you mean if you have three projects open—one is a 150,000 word novel in progress, another is a 3k technical article, and the third is your general purpose notes and ideas project with 12k words—and you would open something like Project Statistics (though obviously, with a different menu command than that) and get a readout that says 165,000 words?
No I mean if I have three projects open and I have the Project Target window open. I type 250 words in one, 300 words in another and 450 in the third. I would like the Project Target window to show that I have entered 1,000 words of my 3,000 word quota.
Given the Project Target window would, in essence be, a Projects Target window.
Not sure if this went through the system. I would like to see a universal word count, where you have three projects open and the total word count, counts words from all three projects.
Yes, I got it. If you can see it here we all can. 
There would need to be some mechanism for linking those projects together.
Right now I have 13 Scrivener projects open: one is a letter to my MP, another a letter on an entirely different topic to my local councillor, there are four novel drafts in various stages of completion open (but none of them connected in any way other than that I am the author), a formal specification of a software project, another with various ideas for software projects (none of which are related to the formal spec), a draft of an academic book, a draft for a new character sketch template, a draft political manifesto, a draft of a new settings template, and finally a draft of a short story. Text added to one project is irrelevant to any of the others so an aggregated word count would be meaningless. And what of the Scrivener scratchpad would the updates to that also be included in such an aggregated count? What happens if the scratchpad is closed or any of those (unrelated) projects closed should the aggregate be (re)updated?
All of which is a long-winded way of saying I don’t understand your need for this. Perhaps if you were expand on why you think it is useful. Not that I’m a member of L&L or have any say in what goes into Scrivener but I’m finding it difficult to see why such a feature would be necessary.