We've not heard anything new on this for a long time: this original tweet was a year ago and was talking about "mid next year" which is around... now!
They've been working on this a long time, plenty of time to plan for upscaling for future versions. If they had taken this into account and made it so that things could be easily turned to a higher quality and effects able to turn on and off, it could be fairly simple for them to pump out a higher quality build suitable for PS4/XB1. The PC version might give us some clues there.
I could see potentially a digital-only version being viable fairly soon: there are units out there, but not sure there's enough out there yet to justify a physical run.