I don't really see yet how Shin Buddhism could become even the most popular among Buddhist schools, not to mention in a whole country. That's because of three reasons: 1. requires faith not just in rebirth but in external buddhas too, 2. has no meditation practices that are so popular today and promises no immediate results, 3. reminds many people of Christianity.
"While teachers of the middle way, mind only, transcendent wisdom, mantra, and other schools may have their own assertions, the fulfillment of those intentions is the same. There is not a single thing that is not contained within mind."
(Gampopa to Düsum Khyenpa, in "The First Karmapa", KTD Pub, p254)
“If you recognize the world of appearance and existence as the mind, realize the mind itself as empty, and have no grasping at the superiority of your realizations — this is the ultimate view."
(Chegom Dzongpa, in "The Book of Kadam", Wisdom Pub, p609)