I personally would not see any point in switching. Why would I sell my Chevy if somebody gave me a Ford? Why not keep and drive both, if you can afford it and don't need the money you can get by selling one?
I'd actually be more inclined to sell the new stuff coming to me as it would be, of course, new, and thus bring top dollar.
All my photo equipment is Nikon, except for a Canon camcorder. For video I would go with Canon, consistently, because they have a well deserved good reputation for their video equipment, plus Nikon seems to be ignoring that market anyway, aside from having added video capacity to several of their DSLRs.
That being said, the reason I went with Nikon rather than Canon from the very start was simply that when my mother got a new D40 for Christmas 2007, the D200 was the hot pro level offering. I wanted one but of course couldn't afford it.
Many years later, I found one for 150 dollars at a time when I had several thousand dollars cash in my wallet. And that was the first of MANY Nikons I bought VERY quickly after that, mostly for the purpose of making a small profit, which I did.
But it could have started with a Canon, except I lack even the basic model familiarity needed to know which Canon would be equivalent to the D40 or to the D200. If that had happened, I'd probaby be equipped with Canons exclusively.
It came down to familiarity. I know for certain that Nikon and Canon are solid competitors. You're not going to get screwed if you buy either one. (unless you pay more than retail, of course.) So Nikon won for me, out of simply being more familiar. Now I'm rather well entrenched with Nikon and see no point in spending more money on a different brand in order to get the same photographic results. Especially when you factor in the cost of the additional lenses and other accessories I'd need to buy to duplicate the capabilities of all my Nikon cameras and lenses.
As for the "other" brands, Pentax, Minolta, Konica, etc...to me they're all small fry and while they may be excellent, I am uninterested in them due to substantially reduced product availability and support. You can buy lenses and batteries for ANY Canon or Nikon in ANY camera store in ANY town. With those other brands, that is simply not assured.