One point that is not in the original Guardian article is that this is a proposal only, and a proposal that only applies to French companies that are part of the "Syntec" work agreement.
Yes, in France, companies can adhere to negociated work agreements (named "accord") that define more precisely than the French laws what is possible and is not possible. Syntec is one such agreement, and it pretty much covers the vast majority of IT firms.
Now... What you, gentle reader, need to know, is that that the Syntec agreement is not really that nice to IT employees, as it also defines a lot of things (unpaid overtime, etc.) that are not in the interests of the workers, to say the least. And many IT firms choose not to belong to Syntec, but instead to one of the "accords" that are even more constraining. The company I work with (''it-whose-name-shall-not-ever-be-said-aloud'') belongs to an "accord" that is used to define rules... for the steel industry.
And before anyone starts foaming at the mouth about how French workers are lazy and only work 35h per week: I don't know ANYONE, and I mean ANYONE in France who works 35 hours per week, except maybe a few government employees and McDonald's workers. Yes, I know a lot of people in France who work much longer than that and, yes, I am one of them. Just so you know.