Expose product variation fields to product view display

For sure, this one is already somewhere on the todo list of Bojan. As I couldn't find something in the backlog of the DC issue queue, I'll open this issue anyway ;)

Currently, there is no supported way of showing both the add to cart form and the other fields of a product variation on a product page. You don't even see the price or SKU. You'd have to load the information by yourself and alter entity views / forms and/or implment preprocessing hooks.

In D7 version, the product variation fields are exposed to the parent product display, so you could easily mix up product fields and product variation fields, with configuration only. Think of a two-column layout, where you place the product image (from the variation) in the first column. In the second column you first place the general description text (common for all variations -> field of the product entity), as well as SKU, price (both variation) and of course the add to cart form.

I hope, that we will see this possibility and flexibility also in D8 version.

For now, the lack of some other functionality keeps me struggling in finding a good temporary workaround for this. First of all, I haven't found a successor to the commerce_product_reference_default_product() function - this should not be a great problem, as I guess, that always the first referenced product variation is chosen on the initial page load of a product entity, as long as we don't have the functionality in #2674888: Add a canonical link for product variations committed.

The thing, I miss more at the moment is, that I'm unsure how to compensate the missing hook_commerce_cart_attributes_refresh_alter(): when I render the non-cart fields of a variation by myself, I also have to refresh them on selecting a different variation. I don't want to replace the full Ajax callback that is added by ProductVariationAttributesWidget... Or am I just missing something and it is easier to solve??

Update: product attributes

I've just tried the new product attributes of Commerce. These are fieldable entities too, which is nice and powerful per se. But currently, nothing really happens in frontend, when you add a field to an attribute. These values get never displayed in frontend. Again, one would like to have the possiblity to include it somewhere in the product template, outside of the add to cart form, updated with every changed variation selection.