PhoneGap will work great from iOS 8 and Android L. Previously iOS and Android's webviews were very slow; from these releases they will be GPU-accelerated with WebGL support and full-speed Javascript. See https://www.scirra.com/blog/146/webgl-arrives-on-ios-8-and-more.
Ejecta will more or less be obsolete after iOS 8; it will still cover older versions of iOS, but since iOS updates tend to reach about 90% distribution pretty quickly, I think it would be wise to simply target iOS 8+ only and enjoy the far better compatibility with a real browser engine.
Crosswalk will still be useful for a while after Android L's release, since Android updates take such a long time to propagate. Until Android L+ reaches vast majority marketshare (like Android 4+ is only just achieving recently), Crosswalk will be the way to use a real browser engine to reach all Android 4+ systems. Hopefully their ads+iap support will come soon, they tell me it's effectively ready but needs to sort out some legal issues (don't know what those might be).
Eventually though in the long term PhoneGap will basically cover both platforms with excellent performance and support.
IAP support is already coded in for Ejecta, if there's a problem with it then please file a bug report!