(cracks knuckles)
- It looks to me that in O that there is no universal remote and each of the systems are proprietary, meaning that DCS only works with MTH locos, LionChief+ with Lionel, etc., correct?
That's correct. These systems were developed by competing companies for their own product, rather than a standard imposed on them by a third party (i.e. the NMRA)
- So therefore, I will have to get a control system from MTH, Lionel, Bachmann (aka lots of $$$$) so that I run locos from each company?
At the moment, it means two systems: Legacy/TMCC and DCS. You can operate a TMCC control box thru DCS as the codes for TMCC were made public. The additional codes under Legacy were not. Having Legacy locomotives means you would need a Legacy setup to reach all the features of Legacy units. Bachmann's system hasn't been added to their O-Gauge line.
- Or am I pigeonholed into buying locos from one manufacturer only and stick with them until eternity? I hope not.
Only if you want to. There are some here who do that. I'm sure you'll hear from them eventually 
- Can my older locos be made remote compatible by simply adding a decoder chip?
Yes. The cheapest method right now is to add a TMCC board from Electric RR Co. (about $70). Adding sound requires a secondary board ($85). A DCS upgrade board is available, but is considerably more expensive, and requires the locomotive in question to have flywheel motors.
- Do LionChief+ locos work on tracks other than FasTrack?
LionChief is just radio control using track power instead of batteries, so it doesn't care who's track it's running on, or any other command systems hooked to that track.
Your proposed M-7 upgrade is a little more problematic. Lionel apparently designed the M7 as a dead-end product: without swapping parts around, you can only run it as the base set plus two-car add-on (and it's not clear they anticipated any six-car operation when they designed the power car since the LionChief set only has three cars). You will have to make substantial modifications to one of your power cars' chassis in order to run both of them in the same train.
---PCJ
