A capital is about more than just where the parliament sits. Whatever happens to the Palace of Westminster, moving the capital out of London is likely to be highly disruptive, while having the political and administrative centres separate is going to be very difficult to manage and will risk significant loss of experience. This will be especially true if there is any kind of crisis.
Considering the OP, I notice that the countries listed (Canada, the US, Switzerland and Australia) all (a) have federal systems and (b) have their parliaments and civil services in the same place.
If the government can make "No 10 North" work under real pressure, then I might change my view - but would still see this as fundamentally a distraction which would not be an investment in the capacity of the country, but an expense in how it's run.