Is the 21st cen Hindu less ethnocentric and more belief-oriented than the 20th cen Hindu?
I think yes
Not today
E.g. An Iyengar would still rather marry an Iyer than a Swaminarayan non brahmin follower from Gujarat
So the relative ethnic proximity of Iyers still makes them more favored marital partners than say the Gujarati Vaishnavas
A GauDiya Vaishnava from Bengal likelier to marry a Shakta Bengali than a Madhwa from the South
Doesn't seem likely to happen in near future either
Yet the Tulsi >> Kamala preference on twitter might be a sign of things to come