Adding Custom Fields to product modules

Hi,

That's more complex. But not impossible. You would need to edit the view file and add a second add to cart button based on the id of another product. It's definitely not just two lines of code...

On a side note, shouldn't you have also two prices for each product ?

In that case, that would mean to redo completely all the listing of products to load all the data, all the characteristics, all the options, etc of all the products displayed on the page.
We didn't do it for two main reasons:
First, that would mean a heavy demand on resources and would mean that you wouldn't be able to handle as much products as actually for listings of products which we deemed more important.
Second, that would mean that the code would be more complex on the products listing. It is already quite complex like that.