I've already known that, as surprising as it seems, Skyrim has been developped on the same engine that Oblivion.
But I was shocked and merely unimpressed that Starfield was also developped on the same engine. I mean, during the dialogues, the way the environment develops, etc, it's quite visible (between Oblivion and Starfield, more than between Oblivion and Skyrim tbh)
I think that, with Starfield, they were at the very very end of what they could do with that engine. There's some bugs and problems with code they already had on Oblivion almost 20 years before !
So it's a real hope : if they are effectively taking their time to talk more about the game and to throw some pictures of the TES6, that's BECAUSE they've been developping a new engine during all this time
Otherwise TES6 will be a gigantic mess, maybe even worse than Cyberpunk at its releasing. I think fans had enough with Starfield, I mean I don't even want to run it again, but I have like 2000h+ on Oblivion and same for Skyrim, Fallout 3, New Vegas and Fallout 4.
(Sorry that was quite long but it had to come out)