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.
"If the Buddha-Nature is seen, there will be no seeing of a nature in any thing."
(Nirvana Sutra, T12n374p521b3; tr Yamamoto)
"Neither cultivation nor seated meditation — this is the pure Chan of Tathagata."
(Mazu Daoyi, X1321p3b23; tr. Jinhua Jia)
“Don’t rashly seek the true Buddha;
True Buddha can’t be found.
Does marvelous nature and spirit
Need tempering or refinement?
Mind is this mind carefree;
This face, the face at birth."
(Nanyue Mingzan: Enjoying the Way, tr. Jeff Shore; T2076p461b24-26)