Hari you can change the default and maximum number of results returned by an API request, but there's no way to make it really infinite.
Also the discussion scroll logic might have trouble dealing with "pages" with a greater number of posts.
Most likely to change this you will need to extend the javascript code of the PostStream, the pages logic of ShowDiscussionController and the default/max limit on the ListPostController. I think the last two can be achieved with the Extend\ApiController extender. The first one I'm not sure if it's required.
I don't remember seeing any extension customizing it.