If the the Surface Pro (5) with LTE is any indication, it will most likely have both a Nano Sim slot and e sim support, as the benefit of a merged core is that code is almost ubiqitious. Meaning if the Surface Pro with LTE supports it then other devices could support it as well through appropriate code modifications.
However
@xandros9 has stated, the device will have to exist as changes can still happen last minute i.e Surface Mini Cancellation.