Assuming the train services is reliable & the charges are competitve, it might be a benefit to Sporeans.
Many Sporeans will be retired by then & they can take advantage of the cheaper living costs in Malaysia. They will not be limited to just JB but can look at Malacca, KL, Penang, ... These people only need to return to Spore to collect the rent.
With the way things are going downhill in Spore, the PAP might face a situation where Sporeans are abandoning Spore to go & live in Malaysia

Just look at the problems Orchard Road is having with the high rentals. You can find the same things in KL for cheaper
Malaysia also has cheaper medical care than Spore, with fewer medical staff from the 3rd world. If you live in Malaysia you don't need to pay for an expensive COE, expensive fuel, electrcity,.. etc