If anything just buy online. Better stock (most of the time) and almost always better prices. Also, how often are you really buying lenses? You have a great setup as it is and I cant imagine you are needing to run out and buy lenses constantly. Its all up to you, and of course you can do as you like ( ), but when you think about it for most I would not think that would be a huge deal.
Saying Canon has stock issues is also funny in comparison to Nikon for me as Nikon is the one that usually releases something and then it is not available widely for months and months and sometimes even years! (take the 18-200VR for example)
Either way, do what makes you happy. If that is switching to Nikon, go for it!