Most used commenting system is (probably) Disqus right now. But there are some very bad disadvantages of it.
One of them is speed. Speed is crucial when it comes to SEO. I've made some tests in my brand new WordPress site with and without Disqus.
With Disqus, client makes 102 requests to the server instead 11. Most of these requests are goes to third-party such as Facebook, Google and their big list of "Advertising Partners".
Another disadvantage is privacy. Simply, Disqus is not privacy friendly.
Another disadvantage is their ads. Disqus charges $10/month for fully disabling ads.
My intention is to create a privacy focused, lightweight but good looking, customizable commenting system with additional key features (that I have in my mind) that helps SEO.
How do you plan to solve the privacy problem?
Not placing tracking links on embed code and not displaying ads and not saving IP addresses to database before commenting should be enough I think.
There's no way to know if you're saving user data or not, but that probably isn't a deal-breaker for something like a commenting system.
I think the idea has a potential.