Agreed. SPs should and can make great authors.There are probably a lot more than you think - I think it's best not to judge all ESTPs as simply "doing" folks who can't write. I'm sure many write, and do (think of all the business and self-help books out on the market). And co-writing? Co-writing is one of the easiest things you can do, depending on who the (famous) person is. It's all about ideas, baby! Shatner might dictate his ideas, or he might scribble down a few notes of what he'd like to see. Then a writer writes what Shatner wants. Shatner reads it over, makes adjustments and edits, and voila - he "co-wrote" a book. I doubt he has the time to sit down and just write a book, with all his acting and commercial deals.
Not nagging on you, though - I love me some Shatner, and I'm a Trekker from way back. But co-writing a book shouldn't be a determining factor of whether someone is a Sensor or an iNtuitive. In the real world there are several ways to co-write something, and any type can co-write.
And truthfully, Shatner might have some very strong intuitive processes. But is intuitive his default? I don't think so. I think he can draw on his intuition when he acts and I think he can draw upon it in different circumstances, but I don't think it's who he truly is.