I'm on a facebook page with a whole bunch of other indie devs making games for Xbox One but who don't have devkits. It's been quite useful chatting to them and seeing what other people are doing who aren't necessarily "on the inside".
The general consensus is that for most, it'll be a case of waiting for the day when MS flip the switch and you can use your retail Xbox One as a devkit. However, the info we've got from ID@Xbox is that games made in c++/Windows8/DirectX11 and also in Unity will be supported. So basically, most devs can get on with making their games and get all the non-hardware dependent bits ready for that day. For some, that might be 90% of the work anyway. So in essence, aside from these 30 devs announced today, and presumably a handful of others as well who are keeping quiet, the starting gun has already fired for being on the first wave of indie games/devs to hit the platform some time next year