I look at it this way. You may not want to just look at the affordability of the properties to the local Johoreans! Iskandar is a different place than say Penang or Ipoh, where that assessment is more applicable. It is next to Singapore which makes it a totally different ballgame. There are reportedly about 1/2 million Malaysians working in Singapore, and more Singaporeans and expatriates in Singapore are also now more prepared to stay in JB and travel to Singapore to work daily. There are already in fact many who are doing just that. This is a large pool of people for potential property market there, not to talk about people from China, Japan and other countries who have also started to purchase properties in Iskandar.
What it means is make sure your properties purchased are high-end and at choice locations which are attractive to this group of people for both sale and rental in near future. You cannot depend on local residents. Most of them can't afford these properties. But JB is just next to a global city currently with 5.3 million residents, many of whom can easily afford to buy or rent these properties with Ringgit so low. It is also on the radar screen of international investors because of its proximity to Singapore. Besides there are already also expatriates in the Pasir Gudang industrial area paying good rentals for good properties. The commercial and educational and medical facilities planned for Nusajaya side hopefully will also attract more expatriates for the rental market in future. The picture is thus not that unfavourable even for rental market, provided of course your properties are attractive and at good locations. Of course, if and when the MRT really connects to JB (?), the picture should be even rosier.