While, it is really easy to move from GMail to Outlook.com mail service, I don't think that should be the strategy from Microsoft.
In GMail you can enable POP, and go to Outlook.com and settings enable to read from GMail.
It works fine.
My Outlook.com has transferred all my GMails (from 2004) to my Outlook.com.
All the new GMails appear in the Outlook.com.
In you "From Address", it will say "Sent only behalf of
your@gmail.com".
Not a bad solution.
Additionally, you can create an Outlook.com mail alias also.
And you can use any mail id interchangeably.
But, it is good solution for everyone out there.
People love gmail.
So, if you asking them to move from GMail to Outlook for Window Phone, it is going to fail.
I am sure, MS is aware of it.
And they will have a solution (like Apple).
So, you folks who don't want to use Outook.com you don't have to worry.