Let's have a look at a few examples of quote splicing:

val a1  = List(1, 2)
q”..$a1" // ==> q”1; 2"

val a2 = List(1, 2)
q”$a2"   // ==> q”scala.collection.immutable.List(1, 2)"

val b1 = List(q”a", q”b”)
q”..$b1” // ==> q”a; b"

val b2 = List(q”a", q”b”)
q”$b2" 
// now   ==> fails
// opt A ==> q”scala.collection.immutable.List(a, b)” 
// opt B ==> q"scala.collection.immutable.List(Ident(TermName("a")), Ident(TermName("b")))

Last example will work if we provide standard Liftable for trees which will essentially be an identity function (option A). This would be consistent with how lifting and splicing works in quasiquotes.

Another approach might be to lift trees as their reified equivalents (option B). But I don't expect this being needed by anyone apart from extremely advanced users and it would be quite surprising for everybody else. This will also be hard to implement considering that reification of trees as trees requires passing target universe somehow.