A lot will depend on why you need cross-platform support at launch. For most direct to consumer apps, your intended user base should skew to one platform or the other and should be large enough to support a beta and launch on a single platform. Not launching with both platforms supported won't make or break your app and launching with both without much mobile experience to begin with could even prove to be a distraction while you try to iterate on you're app's design.
If you're selling an app to businesses, then not supporting both iOS and Android at launch would be a real roadblock. In that case starting and maybe even staying with Ionic could make sense.