It seems that there are two major issues at play here:
The first was addressed above, but I'll repeat it anyway, While bluetooth technology makes battery power a more practical option, battery power and Bluetooth are two seperate, distinct, technologies, and while they can be used together for those that want to, there is no need to do so to gain the benifits of one or the other. You could run Battery power TMCC if you wanted... Not sure about DCS, as the signal is transmitted through the track power.
The second issue is the capabilities of BlueTooth it's self. It seems people think that the limited functions from a smart phone are all this technology can do, to which they are mistaken. The only real short coming of bluetooth being used for model trains is that the max range is going to be limited... unless the system was designed for and implemented signal repeaters.
I think most people associate Bluetooth with running a train from your phone, and while that is an option, you can use bluetooth without a phone at all. Bluetooth is simply the name of the encoding system used over 2.4GHz wireless radios, and is at least the most common, if not the best such system. Other similar radio protocols would be Wifi, or on the very simple end, LionChief plus, or using the same radios, Microsoft and logitech wireless keyboards and mice.
As to having to "rip out" the electronics in engines, I'm unsure why this would be the case , at least in most TMCC locomotives. One could design a replacement R2(4)LC board that pops into the same socket and uses bluetooth communication instead of the 455K track signal, preserving all of the engines functions.
I guess it comes down to understanding that there is a difference in the implementation/apparatus, the user interface, as it were, versus the underlying technology. A TMCC system, if fully exploited is capable of sending 65,536 unique commands. In practice it can make use of much less. Legacy improves on this with about 4 times as many commands available to the system, plus multi-word commands. A single data packet over bluetooth contains at least 4 billion bits of information, and the standard packet size of 32 bytes is a 1 followed by about 70 zeros of information. So, while the current implementation of bluetooth for trains has limited features, the technology it's self is practically limitless in the features it could operate. Add to that that bluetooth is self error correcting, meaning that if the information sent isn't received perfectly it knows there is a problem and can act on that. Also, each device will have a unique id, meaning there is no chance that multiple clubs will have overlapping signal issues, or such.
The only downside to this tech that I can see is the "short" range that may be a problem for large club layouts and the like. This could be solved very easily with range extenders, though this may require a bit of additional programing to implement.
All told, Bluetooth (or any other digital, error correcting, 2.4GHz radio for that matter) is just flat out superior to an analog track signal. It is only the apparatus that is lacking in features, not the underlying technology.
JGL
P.S. That Legacy system everyone loves so much: yeah, the thing talks to and provides all those functions with a simple 2.4GHz communication from the remote to the base, you're already using a dumbed down version of bluetooth if you run Legacy.
