What’s in it for developers? Well, it’s "a new software platform, which fully leverages Nokia’s investments in Smarterphone, which it acquired in 2012". Apps are developed in Java, similar to Series 40 apps development. The ‘new platform’ aspect means there are no apps other than those Nokia convinced (almost certainly paid) to be initially produced. The lack of initial apps might be an opportunity for developers. The larger questions are a) will there will be large market for these phones and b) whether developing markets offer app related revenue opportunities (are the users or companies willing to pay for apps or services).
As of writing this there’s no mention of the new Asha platform on the Nokia developer site which doesn’t communicate the right message for those who might be interested in developing for the platform.
Will this new Asha platform go mass-market? The Asha 501 is a ‘pretty’ phone that has few apps. The current competition is the Samsung Galaxy Y that has the highest smartphone market share (about 18% in India). The Galaxy Y is much uglier but has hundreds of thousands of apps (and 3G for that matter). The outcome might be be related to whether the developing world ends up preferring pretty phones or those that "get the job done".