Leaving out automation (which given you mention arduino or raspberry pi could be used for that), with command control it really hasn't changed. If you want out of the box command control, it is still Legacy and DCS. In terms of why someone would go with these, it is because even now they are simply the only out of the box solutions (I'll get to that). With legacy at the moment (pre base 3.0), you have legacy through the command base, and in legacy 2.0, you also can go bluetooth from an app running on a device to control the engine. (Lionchief , Lionel's 'starter' command control, works via a remote; the later lionchief engines also can work from an App via bluetooth, not sure if lionchief+ or lionchief can work via an app). With Base 3, you can control any lionel command control engine, it will be accessed via wifi using a new app.
For MTH engines, you still need DCS to use them in command mode, using either the old TIU based system, or the new TIU that integrates wifi into it (which also is for the moment going to be app control only , no remote). MTH TIU can connect to a lionel command base and allow controlling lionel engines (I don't know if you connect base 3 to the DCS TIU and if it can control lionchief engines or not, my guess would be no though MTH as far as I know hasn't said anything about lionchief support via base 3). So again, basically no major change.
DCC , which is the standard in 2 rail O and HO/N worlds, is not used much in 3 rail world. MTH supported DCC in its PS 3.0 chip set, prob because some of the engines could work in 2 rail, were convertible. DCC is attractive in that it is an industry standard, it has grown a lot in terms of its functionality, but it is a totally different system than either dcs or legacy.
As others mentioned there is bluerail, which allows for bluetooth control of engines. I don't know if that uses DCC or is its own decoders, but again this is not off the shelf,, you would have to convert engines.
So in a nutshell, it really hasn't changed much in the sense that the DCS/Legacy dichotomy still rules.
