A few days ago Mercedes boss Norbert Haug told German publication Bild am Sonntag that there might be some surprises in store when the new MercedesGP team announced its driver line-up for 2010.

Well yesterday’s confirmation that Nico Rosberg was joining the squad wasn’t exactly the surprise we’d been hoping for. Afterall, it had been a pretty poorly kept secret that the German was bound for Brawn, the only difference between when the news broke in hushed whsiper a few months ago and yesterday’s announcement was the departure of Button to McLaren, which made Rosberg Merc’s new team leader and left a vacant seat next to him.

The surprise therefore is over exactly who will partner Rosberg at Mercedes in 2010.

There’s been a lot of chat over Michael Schumacher making a return with the team which ran him in sportscars 20 years ago. It’s a beautifully romantic idea, but doesn’t add up. Quite apart from his health and the question marks over the strength of his neck, there’s the Ferrari contract, the protestations from Ross Brawn that it is never going to happen, and the confirmation from Michael’s own people that negotiations were never begun.

There are loud rumours that Mercedes will be a German super-team, to combat the English super-team at McLaren, and that Nick Heidfeld is the favourite to land the remaining seat at the team. While he’s hardly Michael Schumacher, Nick’s a safe and fairly quick pair of hands. He is an underwhelming choice however and hardly fulfils the promise of a shock.

Who, then, suits that description?

If Mercedes is still reeling from its failure to grab German wonder kids Vettel or Hulkenberg, they may well have their sights set on Adrian Sutil. At 26 he is still pretty young, and with the last year racing at Force India he has an understanding of the Mercedes powerplant. He’s marketable, like Rosberg, but one feels that Mercedes Grand Prix in 2010 would probably be a bit too pretty with both of them on board. They might as well rename the team Premadonna Grand Prix. No, I jest. They’re both solid, hard working guys. But are they a mega line-up? In all honesty, they are not a Hamilton / Button. Sutil still makes too many mistakes, and Rosberg still fails to get the most out of his cars.

Today’s announcement, then, that Force India will be testing Paul di Resta and JR Hildebrand in the rookie test days at Jerez could be a little more than appears at first sight.

First of all the announcement shows that Vijay Mallya’s promise to bring an Indian racing driver to F1 was worth fairly little. The team ran Hildebrand, Neel Jani and Karun Chandhok through a simulator test and promised a seat at the rookie test to the quickest driver. My sources tell me Chandhok was quickest, followed by Jani, and Hildebrand was plum last, by a fair margin. Jani (half Indian) and Chandhok (properly Indian) have both been passed over for the slower man. I’d wager it had something to do with finance. So much for your promise, Vijay.

The second driver at the test however is down to the team’s engine deal with Mercedes. Could Merc be using this test day to evaluate Paul di Resta for promotion to Formula 1? Could it be a genuine shot for the Scotsman?

Tonio Liuzzi has a deal to race for Force India next season. The team will have one spare seat, which looks likely to go to Sutil if he doesn’t go to Mercedes, and with Hildebrand and his finances looking good for the third driver seat at Force India or possibly even USF1, what are the chances that it is di Resta that ends up at Mercedes alongside Rosberg in 2010?

Don’t forget that di Resta beat Vettel to the F3 EuroSeries crown in 2006. His credentials are outstanding, but I have always questioned Mercedes’ common sense (or distinct lack of) in thrusting brilliant single-seater talent into DTM. how is one supposed to prepare for the pinnacle of single seater racing in closed wheel motorsport? Doesn’t make sense, does it?

There is one other possibility, however. Recent comments out of Renault boss Carlos Ghosn suggest all is not well chez Renault. The prospect of the team pulling out of F1 if it does not find a buyer for the team (or at least a substantial percentage investor) grows ever stronger. And if it does, that puts Robert Kubica back on the market. Could it be that Mercedes is simply playing the waiting game for the highly rated Pole? It’s not out of the realms of possibility.

So could di Resta be the shock Mercedes have promised? Will it be Sutil? Will we see the romantic return of Michael Schumacher or could Robert Kubica be with his third team in as many months?

It’s the only really big question left in this winter’s driver market. I just hope that the surprise is as big as we’re wishing.