Dependencies in product attributes

I want to add several attributes to a product variant.

For example:

Attribute1 = Rad
Posible values = 8.5 and 8.7
Attribute2 = Pot
Posible values = If attribute1 = 8.5 some values, and if attribute1 = 8.7 other values.

I know this can't be done right now and probably there is no plan in supporting it. However... can you please give me any advice in how to implement it?

Also, as I have read in other threads, the SKU should be unique for each product variant and combination of attribute values, if not it doesn't make sense because you can't control stock that way. Is there any plan to fix this in the next version?

Thanks.