The problems you are going to face are:
1) you need a good package delimitation, with clear contracts (on which package/API do I depend?) both in the Squeak image (to save the package that you want to see reloaded) and in Pharo
2) the package delimitation has to be in good agreement, because the MC tools do not deal with package refactoring
3) since API are not in agreement, you gonna need plenty of glue for working around changes like trimBoth, includesSubstring: etc...
What are your goals exactly?
A) you want to build on top of smaller kernel?
Then once you have 1), why should you go into Pharo rather than building on top of your Squeak kernel?
B) you want to profit by clean-ups and refactorings and shiny new architecture made in Pharo?
Then yes, porting some interesting Squeak bits to Pharo has some value.
But that means you spend a lot of efforts for maintaining those bits alive.
That means switching from old file system to new one, switching from old text system to (yet future) new one, switching to Spec, switching to Settings, Announcements etc...
C) You have no specific goals, just want to follow the momentum, but keep your confortable Squeak slippers?
If you end up with hacks for loading all the old Squeak mud, then you'll end up with Squeak, just a different Squeak, and unless you enjoy jumping many hurdles, I don't see the point.