"Is there any way that Scirra can develop some quality solutions that will work as they shud... leaderboards, in app purchases etc?"
There is no specification for Google Leader boards. Also you can use Browser.execjs to use JS api's without writing your own plugin. I have a FGL pure CAPX implementation of their SDK. Including FGL leaderboard. If you have AJAX support you have access to the creation of leaderboards.
I have said it before. But sometimes it's time to pull up the sleeves are create it. R0j0, Rex, Luna, Kyratic and many others write Plugins to access JS functionality. That's the point of the SDK. If it's missing and some one needs access to it, then they have options. Scirra doesn't need to create everything for the users. there are other that cover those.
Also Scirra provides an Arcade score for their own score system.
Scirra also provides the IAP for a handful of stores and I'm pretty sure there other non Scirra plugins that support other stores.
As a piece of information. In store purchases for say Unity don't have Unity support for IAP. All Unity developers who are doing IAP have to use 3rd party apps that they pay for or create there own. Only Unity5(not out yet) will support IAP. So really C2/Scirra are providing a massive load of features already in comparison t other big name tool sets.