It's going to be about another 12 months before the new consoles launch. As with any new hardware, there will be some bugs to iron out in the first 6 months and people will typically wait to see what exclusives that Sony and Microsoft have. Also, even with a good lead in, the demand will be well above supply, as seen with the Switches launch and famously, the Wii.
From what I have read about the consoles, is that their hardware is almost identical, which should really aid "SE" in streamlining the two consoles updates. Another thing I remember coming across is that from . a programming point of view, the new consoles are now an evolution from the previous generation,as they are using a more "standard" architecture, which makes it easy to write code for. Finally, both consoles will have full backwards compatibility, so as long as they have an XBone version, they will cover both consoles as the XBone is phased out.