Q:

A way to prepend letters to each imported class

Is there a way to import all classes from a package and rename them all by prepending some text? A construct 
import packages.{_ => Abc_}

compiles but seems not to be doing that thing.

A:

It's not exactly what you're after, but if you can put up with an extra . character, you could write
import com.{packages=>Abc}
val x:Abc.Whatever = new Abc.Whatever(...)

A:

No, no way to do such a thing.
"Programming in Scala, 2nd Edition" 13.3, which is 2.9 based, defines the rules.  I don't recall anything in the changes for 2.10 that alters the import mechanism.
Given import package.{selector}, selector may be one of:

x, a simple name
x => y, renaming x to y
x -> _, hiding x - excludes from names imported
_, the catch-all - import all names.

That's it.  Your variant looks interesting, but isn't in that list.  It is interesting that {_ => ...} compiles for various values of ..., but it's not clear that the effect is any different than _ for the few trials I ran.

