Sophia is beautiful and classic, so I doubt it will ever entirely fall out of style. It's one of those timeless names that can never be trendy or relegated to a specific decade. As for being too popular...I know the SSA has it high on their Top 1000 list, but I suspect if you added up every variation of
Isabella,
Caitlin,
Madison,
Addison, [insert tryndee name here], and
Sophia, and then compared them,
Sophia would fall much further down the list.