I have only briefly experimented with it but in the latest FX cameras (e.g. D810) the "dynamic 51-point 3D" or whatever it is called is fairly well able to maintain focus on a subject in those cameras which have higher resolution matrix meters. I think it would be possible to first point the manually selected point to the bird once and activate the focusing, then as the bird turns its head, just turn the camera to recompose the shot and let the camera take care of finding where the bird is in the frame (within the area covered by the AF sensor array). It might not work 100% of the time but neither does single point focusing. It's worth trying it if you have one of the 2014 cameras.
The D4(s) doesn't have an AF-L/AE-L button to reprogram. Although I don't feel the need for two thumb buttons, if they can be reprogrammed in a flexible way, it may find uses.
I don't think an increased AF point spread is possible, unless it is based on focusing using the main imaging sensor, which in turn has its limitations. However, what Nikon might be persuaded to do is increase the spread of cross-type sensors, although in the latest interviews they seemed to regard that there is a compromise between achieving low light sensitivity and a lot of cross type sensors, and they seemed to prefer a layout where low light sensitivity of the focusing is optimized.
One way to solve the need to have larger focus point spread is to use a high resolution camera such as D810, and when required, compose in such a way that you can achieve a very-off-center composition by cropping a bit from one or two sides; this typically requires no more than (say) 10-30% of the image area to be lost, and with a 36MP sensor you still have 24MP or more (maybe next year we will have 50+MP, so there is even less damage). The 1.2X crop mode on the D810 is also something that can be used and works quite well. Finally there is the D7200, although that camera seems to have a lower resolution matrix meter which can affect the performance of the automatic subject recognition and tracking, if you want to use that.