A possible split in the PAP, which has been mentioned a few times by other people, seems quite unlikely to me. Because Tan Cheng Bock said some PAP grassroot people indicated that they had supported him during the presidential election, others think that a split in the PAP is a real possibility. In the power dynamics, PAP grassroot activists are unimportant and irrelevant. The attitude of the grassroots is not central to what happens within the PAP. The structure within the party that either shows unity or fissures is the CEC and the mass of cadres. Members who have been inducted as cadres have been done so for their political loyalty more than anything else. Thus far, no-one has been able to point to any ordinary cadres, let alone CEC members, who have said or written anything that is a divergence from the party line.
Actually, most one-party regimes do not transit to multi-party culture by splits.
In Japan, LDP's dominance was reduced by DPJ which was not a split from LDP.
In India, Congress's dominance was reduced by BJP which was not a split from Congress.
In Malaysia, BN's dominance was reduced by Pakatan which was not a split from BN except maybe a small part. PKR took in many members from UMNO and MCA.
In Cambodia, Funcinpec's dominance was reduced by CPP which became dominant and was reduced by CNRP, all which were not splits.
In fact, most splits of the major party did not succeed.
In Singapore, Barisan split from PAP but did not manage to unseat it.
In Malaysia, S46 split from UMNO but did not manage to unseat it.
In Japan, Japan Renewal Party split from LDP but did not manage to unseat it.