Nico Rosberg, Vettel's potential teammate for that year, told Britain's Sky he thought speculating about two years' time was "not silly, it's what comes after silly".
Others think it's just contract extension time.
Vettel is firmly under contract to Red Bull for another year, so - as a quadruple world champion - perhaps he is just lighting a rumour or two to drive up his price.
"I think Sebastian Vettel is playing very clever contract poker, just as Adrian Newey did a few weeks ago," former F1 driver Alex Wurz told Germany's Sky in Hungary.
Indeed, the ever plain-speaking Niki Lauda moved to rubbish the speculation altogether.
"We have never talked with Vettel about a contract or a cooperation," the Mercedes team chairman told Auto Motor und Sport.
"Why? Because we have two drivers.
"We have just extended the contract with Nico, and with Lewis (Hamilton) we are talking now. There is the desire to extend his contract as well.
"It makes no sense for us to look for a new driver," Lauda added, insisting that is also true even if Fernando Alonso was on the market.
Amazingly, a wild rumour has been floating around that Spaniard Alonso made a visit to Williams' Grove factory recently.
Actually, he did -- Sir Frank Williams is an aviation enthusiast, and 58-year-old, Madrid-born Fernando Alonso is a top Airbus official.
Lauda advises the 32-year-old Ferrari driving-Alonso to stay put.
"If he has performance clauses in his contract that allow him to go where he wants, where could he go?" the great Austrian said.
"He can't go to Mercedes. Back to McLaren with an engine he cannot judge beforehand? That's a big risk."