It was always said the older SMEG units don't have the necessary hardware to support this, so there's no way you could do it just by updating software. I do believe this to be true, since if the necessary hardware was there, Peugeot itself would announce it and instruct its partners to enable it to users for free, since it would be a considerable selling point, and if everything you need to do is to flash the unit with newer firmware - that's a no-brainer, quick and simple win.
So no, I don't believe it's possible to do on older units.
While it would be such a nice thing if I could somehow enable CarPlay on my 2014 car, I too also believe it's highly unlikely this'd be possible just through any kind of software update.
I've always read that the newer cars that support it have a new/different SMEG unit.
I know from personal experience that SMEG units are different with regards to navigation. Car that doesn't have the navigation have different SMEG unit. And it's not the GPS antenna because that one is located on the roof. OK, you'd need antenna and pay for maps etc, but hardware-wise I'd say units would be identical, maybe just the nav option is disabled via software. But no, that's not the case - to enable nav in a Pug (2015) that didn't have it factory-enabled I had to change SMEG, activate options in car's computer, change roof antenna and cable from antenna to SMEG. Go figure...