I think this is a smart bet. Especially when they teased it by saying the first stage of getting their engine to run on current gen consoles for Fallout 4 was by porting Skyrim to the Xbox One. Sounds like a lot of the leg work was already done this time last year.
Regarding TES6, all we know is it's been in development since 2011 with the trademark "Redguard", with that trademark having been renewed multiple times since then and still being listed as active. To do so requires proof of work in progress to the relevant authorities since it isn't a commercially available game, which is also how we know it isn't related to the old "TES Adventures" game of the same name (other old TES games no longer commercially available all have dead trademarks, such as Battlespire, Arena, Daggerfall). We know Todd only has one team, with one game in full production, and usually one in pre-production, though it sounds like the team now has two games in pre-production with the talk of a new IP.
So safe bets for Bethesda Game Studios are TES6: Redguard in full development with a late 2018 release date, with Fallout 5 and a new IP in pre-production, likely with the new IP coming first. Bonus bet for outsourcing another Fallout game to Obsidian to plug the gap until Fallout 5.