They'll probably just wait until there's a sufficient number of Xbox One Arcade titles to release those as the free games for gold. Nobody said they'd be giving out 360 games for the Xbox One, just that the service would continue [b]on[/b] the Xbox One.
[quote]"Great news: Access to free games each month is coming for Xbox Live Gold members on #XboxOne – Details coming later in 2014[/quote] They haven't announced any date for when the Games for Gold benefits will begin, just some time "later in 2014". By that time there will likely be some XBLA games out for them to give away.
Oh and don't forget that there'll be separate titles for the Xbox 360, so that'll continue also. If you have both consoles, that is four free games per month. Two or three of which will probably be shit but oh well...