If OP just wants religions “to register as 501c3’s”, then I believe they already have almost what they want. From what I understand, the principal tax exemption available to religious groups under US federal income tax law is 501(c)(3)
It is true that religious groups get their 501(c)(3) status automatically without having to apply for it to the IRS - but changing that rule wouldn’t lead to them paying any more tax, since if they do apply the IRS almost always just grants it anyway.
