I want you to try a quick thought experiment to help you understand where the state of religion is at.
Ask yourself: Would you ever hear someone 300 years ago say “I’m Christian but believe in Karma”, let alone hundreds or thousands of people saying this?
Mixing beliefs between religions was pretty much unheard of. There was a strict homogeneity in them that prevented nearly all possible mixing of belief systems. The biggest causes of erosion, in my opinion, to that homogeneity, is melting-pot countries, and technology (especially the internet).
Melting-pot situations force people to first accept other people’s beliefs, and then to possibly inherit them. It only takes a situation as simple as a Christian and a Pagan getting married to cause a mixing of beliefs in not just the child, but the parents as well. Of course this situation could very well be met with force by the prolific and violent Christians of the time, but eventually love and life have their way and foreign beliefs become entangled in the culture.
300 years ago you wouldn’t hear a Christian declaring Buddhist tendencies, but today it’s quite popular, and the trend continues through many other religions. We are, and have been, living in the age of Open Source Religion. We are not moving into the age of Open Source Religion. It is already here. We are moving into an age where we realize Open Source Religion exists, and are conscientiously utilizing it.