I want to add one more reply to this thread, in hopes that someone from Lionel or MTH reads it. I'm sensing a lost opportunity here. Although most of us lack the skills to build a loco from scratch, there's a subset of model railroaders who stay with it because they like tinkering, and even full-on customization. So it's a letdown that the majority of locos are designed in a way that frustrates even folks with advanced mechanical skills.
IMO Lionel should encourage, empower, enable this kind of tinkering. Every loco should have a modular interface for its motor, gearbox, replaceable wheels and axles, electronics, optional add-on detailing kits, etc. Some examples might be a high- and a low-speed worm gear; axles with or without grooves for rubber tires; Boxpok or spoked driving wheel assemblies; alternate pilots, feedwater heaters, boiler fronts, etc. Maybe they could even release a couple of "screwdriver assembly" kits like the vaunted 700K of the 1930s. As the prime model railroading demographic ages, larger scales really lend themselves to this type of thing. But please, no restricted parts availability out of fear that someone will "build a Vision Line whatever out of parts" and sell it as a counterfeit.
Ideally when someone buys a starter set loco, it shouldn't quickly become obsolete or outclassed. There should be an upgrade path, which endorses and reinforces the original purchase decision. I believe Lionel, MTH, etc., should embrace these philosophies, for both their own continuity and the good of the hobby as a whole. My $.02.
