"Building it into Legacy is an option, but now the cost is in the range of your point regarding MTH. (The Legacy system is $280 and the Legacy WiFi is $165, so $445 plus cables, and I make be missing some components.)"
The only reason for Lionel to do this is to please Legacy users who want to be able to control most Lionel products using their Legacy system. Those starting out without Legacy will have command control simply by using their LionChief remote, which comes with the loco/set, or using the Bluetooth app. People who don't want or need the features of Legacy need not spring for the Legacy remote/base and wi-fi unit. I'm guessing they will eventually deal with this issue, but I suspect it is a very low priority. The LC and LC+ lines are not presently directed at the serious hobbyist who already has Legacy.
Would not surprise me if at some point in the future all Lionel locos , including Legacy, have the Bluetooth receiver built in, since the additional hardware costs are likely quite modest, and the firmware is sunk costs, as it already has been developed for use with LC/LC+.
