Before answering we should have a understanding about affiliate marketing. It is marketing so it will definitely have a relation with selling of something and also way to sell it.
Affiliate marketing, is a model adopted by the company to market their product through websites or any medium which can brought traffic(customers) to them and in exchange the company pays a certain percentage of commission to the website which is bringing traffic to it.
There are many companies who has adopted these methods examples are Flipkart, Amazon, Shopify etc.
This method is quite active now a days and many companies are adopting it to gain exposure and traffic to their websites, many coupon giving companies are working on affiliating marketing methods.
I guess this method won't get less in popularity in near times as more and more business are going online and this method assure a good traffic, so I think it will work in near future.