I didn't ever get the impression Bill Gates had to somehow work really hard in order to market his company. In fact, he wasn't a sit-back and observe Five-type thinker; while he could do code/tech stuff, his approach to Microsoft was to see opportunity, cobble together smaller programs and work by other people, then aggressively market the resulting product suite. I would have said he was more of a 7 or 8 to begin with.
I actually have experienced a large shift from a 5 pattern toward 8. When I was 20, I was very detached, observant, non-engaging, excluded emotion, and never chose to act (mostly because I wasn't ever really driven to make a decision). What happened in the second part of my life is that I finally realized the need to engage life rather than remaining passive and powerless, and use the things I had observed and pieced together in order to interact with others. I used to always back down or be diplomatic, but nowadays I find myself sometimes digging in and going face to face with someone, if I believe it is necessary. It's 8 influencing 5, since at core I still favor an "analyze from a distance" approach and the clarity informs my actions, but regardless of any anxiety I feel over conflict, I still often find myself standing up to something rather than just avoiding it as I used to. That seems to be what Riso describes as 5 moving toward 8 ... no longer remaining an observer, but a participant who can use one's knowledge to accomplish things that one believes to be important.