How hard wil be the migration from CI 2.0 to 3.0

[eluser]anis2505[/eluser]
Hi as the title says

I'm starting a new project using 2.1.3( because CI 3.0 future still unknown ), for now it's almost CI the standard nothing additional to it.

So when the CI 3.0 will be released how hard will it be to migrating my application to it ????.

Thanks