Frijns’ biggest problem is money. He has said several times that the €500.000 he won from winning the FR2.0 in 2011 was the main reason he could enter FR3.5 in 2012. He has no money for another season in FR3.5, so I think it’s very unlikely he will be in GP2 next year. There aren’t many Dutch companies interested in sponsoring F1 (the Crisis and RenaultF1 ruined ING’s involvement, of which they were pretty proud) and the ones who are (Shell, Philips, Randstad, Unilever) have stated they’d rather focus on teams instead of drivers. McGregor is also closely affiliated with Giedo van der Garde, but unlikely to share sponsorship between Williams and Caterham in F1. Trust, a former Verstappen and Minardi sponsor have been a minor Red Bull sponsor before, but seem to have been dialing back their sponsorship deals. There are some industrials who have a large presence worldwide, but not a lot of companies operate under the same name or product names internationally as in the Netherlands. The breweries are also unlikely to sponsor, since more and more races are ran in Islamic countries, which seems to be the reason a brewery sponsoring Force India ran a different name in some races in 2012.
I think Frijns doesn’t have a lot of options. Sauber was very positive about him after the Young Drivers Test; he needs to spend a lot of time at Sauber and stay fit in case Gutiérrez proves that his idea of not being ready for F1 is more than just a hunch. (Not saying I want that to happen or find it likely, btw.)
DTM might be all he can do in 2013, but I’m doubtful if it’s going to help his career a lot. Spare a few names, future F1 drivers have not always done well in DTM, nor have old F1 drivers. I think he needs to either rob a bank and do GP2 with a front running team, or spend every waking hour in whatever simulator Sauber is using; or have them rent Toyota’s one for him.