I have been searching for some research article to find the benefits of both OTTs and ISPs to collaborate for QoE but I couldn't find some good article which has addressed it clearly. Any help in this regard is highly appreciated.
I understand that you are looking for the business perspective of this collaboration and not the technical advances.
The answer to your question is not straight forward. It depends on the business model you consider. For example does the OTT provider and the ISP is the same business entity? In that case there is collaboration even today. For example part of the ADSL link is reserved for the OTT or IPTV service etc.
But, the question is what happens when the OTT provider and the ISP are two different business entities. In that case the history has shown that they will not collaborate... A big debate has been raised for the so-called network neutrality and the regulation of OTT services by ISPs. I propose to google it and you will find a lot of articles on this topic.
ISPs-OTT collaboration is a very hard subject. In my PhD i work in friendly P2P live streaming systems. In these systems ISPs and P2P providers collaborate to increase QoE and reduces cost of traffic. We called it a win-to-win senario. You can read my conference paper " Constructing a locality aware ISP-friendly peer-to-peer live streaming architecture " or you can read P4P paper "A very good paper in this area" to see the challenges.
Finally, what an ISP will get if it inceases the QoE? it will pay for more traffic.......