Hate to tell you that Singapore has had new citizens turning politician for a very long time. Aline Wong was first elected in 1984, 25 years ago ( quarter of a century for impact). She first came from HK after her husband was posted here. They took up citizenship in view of the HK's handover. She went on to become Minister of State and served 4 terms.
Irene Ng and Ping Pong Lee Bee Wah were born raised and raised in Malaysia, came and did their A levels/Uni here and took up citizenship.
The biggest joke and tells you how much our citizenship is worth is the case of Peter Chen who retired as Shell CEO in Singapore while holding on to PR as a Malaysian. During his entire working life in Singapore, he never felt the need to be a Singapore citizen. He was approached to be the successor to Richard Hu and became a citizen less than a year before contesting and becoming an MP. He was eventually made Sr Minister of State. He failed and went after 1 term.
There are others but if SPH ever carries a story about such relevant things for Singaporeans, sky will just fall flat.
What if one of the PRC turned Singaporean contest for a seat as an opposition? Would he stand a chance?