StackLayout can specify a DataTemplateSelector in its BindableLayout.ItemTemplateSelector :

<StackLayout BindableLayout.ItemsSource="{Binding Source}" 
             BindableLayout.ItemTemplateSelector="{StaticResource TemplateSelector}"/>

BindableLayout.ItemsSource might be a collection containing one item:

Source = new ObservableCollection<Model>
{ 
  model
};

The DataTemplateSelector might be triggered as follows:

Source.Clear();
Source.Add(model);

Sample DataTemplateSelector :

public class TemplateSelector : DataTemplateSelector
{
  public DataTemplate DataTemplate1 { get; set; }

  public DataTemplate DataTemplate2 { get; set; }

  protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
  {
    Model model = item as Model;

    // Determine template; DataTemplate1 or DataTemplate2

    return template;
  }
}

Sample usage in XAML:

<DataTemplate x:Key="DataTemplate1">
...
<DataTemplate x:Key="DataTemplate2">
...
<namespace:TemplateSelector x:Key="TemplateSelector" 
  DataTemplate1="{StaticResource DataTemplate1}" 
  DataTemplate2="{StaticResource DataTemplate2}" />