I think pushing GPS ERP will happen instead of GST, or carbon tax.
Doesn't mean that when they are losing popularity they won't increase
PAP GE winning %
GE1991 61%
GE1997 65% {PAP increased 4% votes} (ERP introduced)
GE2001 75.3% {PAP increased 10.3% votes} (GST increased by 1%)
GE2006 66.6% {PAP decreased 8.7% votes} (GST increased by 2%)
GE2011 60.1% {PAP decreased 6.5% votes}
GE2015 69.9% {PAP increased 9.8 votes}
GST is something that will scare foreigners and foreign investments away.
ERP, carbon tax, etc are hidden taxes.
Example when we talk about Europe exp, we talk about their VAT, not other stuffs.
In the last few years, PAP no need to raise anything new because of more profit from high HDB prices, property taxes and foreigner levies. It's really a lot.
Also the amount of taxes contributed by the 20+% of new population.
So i believe GST should be pretty stable.
It's likely to raise only after the foreigners increase a lot or there's a recession affecting their "profit" from fleeing foreigners.