Gah! I don't think we really know, to be honest, because there isn't much information to work on.
Though I think what you're really asking about is the old sit them early/ sit them late debate. As you'll have seen from the TES discussions, teachers generally don't tend to support the 'sit them early' crew. The reasons for this are, as stated, that there really isn't much benefit to the kids. They do get better grades if they take them later and universities tend to want to see that they can take the pressure of sitting them all at the same time. There is also the big problem of what to do with them afterwards. Yes, you can solve this by getting them to take another qualification, but this obviously only works if they've got top grades in the first one and don't intend to take the same qualification later. The big problem really, is that too many schools do this because parents are impressed by it- and that's really annoying.
However, the other side is that sometimes it can improve their grades. If they're ready to get top grades in a subject in Year 10, why carry on for another year? Yes you will gain maturity and probably benefit in different ways from the subject, but this isn't something tangible you can write on an application form. Also, with some GCSEs removed there is more time to concentrate on improving the grades in others (doesn't work in my opinion- students just start working slower) so it may take the pressure off. There is also the benefit, if some of the exams are modules, that your DS can take them again if he wants to improve his grade.
So what does it mean for your DS? Don't know really. I don't believe universities care that much, to be honest. I would make sure that you get some answers from the school (does it say on their website?), particularly about what they intend to do with the time that they're making up. In my school, that would account for almost 5 hours a week, so it's quite a lot. In terms of whether he's going to get the results this summer or not, it actually depends what specification he's done. Because this is the year when some new specs are coming in, there may not be the option of entering the coursework next year (and thus making it look as though he sat it next year), which would mean he'd get the results this year. This is particularly likely in English.
p.s. Cat64, slightly confused by your post. It's very possible (and probably, if you think so!) that your DS has sat his GCSE Lit and Lang early. I was replying to the OP. Lots of schools rushed it this year, actually, before the new specification came in. Most teachers are so familiar with the old spec that they could teach it to a bright group in a year.