[moonrab]

Malaysia's airlines aren't running up huge profits. It or rather they have to be cheap and affordable for their own people but that's not viable in the medium to long term.

You think about it. Who uses their domestic flight to fly from one city to another? Their own peepur right. How many are Singaporeans? That's a negligible number! 

And despite the already low prices, most Malaysians consider it more affordable to drive or take the long distance buses.

How is the HSR going to breakeven without passengers from Singapore? If you terminate in Johor and make it such a hassle for passengers to have to get off the train and transfer to another mode of transport to travel between Johor and Singapore, then the journey is no longer 90 minutes as touted.

Yes you hit the nail. 
Almost all Malaysian are car owner. Who need a train to travel within Malaysia? 

The hundred thousands of Causeway way commuters are Malaysian or Ex Malaysian, going back to JB. Working in Singapore. Who need the HSR? 

The main objective of HSR for Malaysian politicians, is to build up the stations vicinity infrastructure. Generating GDP. 

Not really for transportation needs.

Therefore Singapore's participation in Malaysia HSR is not the main concern of the project. Other than being a investment point of view, for Foreign Investors interest. 

To Singapore, we are just a last station, similarly to current existing train system. Not much expectation from Malaysia's HSR. Probably more towards enhancing diplomacy with our neighbours. If it is not too costly for our tiny island nation.