Fallout 3 Remaster/Remake most likely. Just a few months ago Bethesda asked some modders who were remaking Fallout 3 in the Fallout 4 engine to stop. This was unusual, as Bethesda has allowed other modders to work on Skyblivion and Skywind, mods which remake Oblivion and Morrowind in the Skyrim engine respectively. There is a strong chance they told them to stop because Bethesda themselves are working on a Fallout 3 Remaster/Remake
Edit: Also, 2018 is the 10 year Anniversary of Fallout 3.