Arel::SelectManager#where_sql が bind_valuesを展開しないのは実装さぼってるだけだと思うの

arel_where_sql_with_bind_values.rb

module Arel
  class SelectManager

    def where_sql_with_bind_values
      return if @ctx.wheres.empty?

      viz = Visitors::WhereSql.new @engine.connection

      binds = bind_values.dup
      binds.map! { |bv| @engine.connection.quote(*bv.reverse) }

      collect  = viz.accept(@ctx, Arel::Collectors::Bind.new)
      collect.substitute_binds(binds).join

      collect.substitute_binds(binds).join
    end
  end
end