At this point I am using busybox and my tc-config and not trying to locate and mount a real root device.
i'm glad tc doesn't have unionfs, it keeps things simple and small and fast like it ought to be. but for the rare occasion that there is a need for an accurate measure of free space by an application (maybe one that can't be recompiled?) or a person that wants it, i hope someone will see it fit to add unionfs or some other option, even if it's an option that few of us want or need, and one that has almost nothing to do with tinycore. (extensions are good.)
you're quick to tell someone that a method they use is "unsupported." it will give some the impression that you're punishing them for doing things their own way, not "the tinycore way," and after years of abuse from microsoft you can't blame them for thinking that, even incorrectly.
better perhaps to say it's not recommended, as you recently told someone that a full install will give him challenges that other people don't have. if they want to proceed, no grudge is beared, and they're free to make things more of a challenge for themselves. you are the author, but the community also provides support, and it seems unrealistic to tell them whether the rest of us will help them or not, even if they do silly things. if we want to help them use tc unconventionally, we should be free to.
if you think unionfs is not a good solution to the problem, that's more relevant than whether you need it, or even that most of us don't. i offered the only solution i know, to install to a mountable device (it doesn't have to be external, but it needs a partition. perhaps there is a virtual partition as a file that you could install to, then copy/merge its contents after installation. i'm thinking of qemu type of image, since iso is read only.)
we're better off for your ideas that make tinycore the way it is, i only hope you don't give people the impression you're telling them they have to use it a certain way, then they might dismiss and miss out on what i think is the best distro ever. i'd rather they feel they have options, even ones that aren't recommended and may create more problems than they solve. that's the way you're supposed to feel using linux, free to take it apart and get dirt under your nails.
tc should be like "tinkertoys for linux... all about having fun." let people have their fun. don't let me give you the impression i think there's anything wrong with putting choke hazard warnings or a note that says "keep tinkertoys away from open flames" on them, i just think you're going to give the very wrong impression that tc isn't fun or free if you always tell them how you use it, as if instructing. i would get that impression too, if i didn't know better. i think you're repeatedly conveying something you don't really mean, along with points i already see the worth of making.
you don't have to draw a line in the sand, between community support and author/design support, or use that to make anyone fear experimentation. if you think something isn't the ideal way, simply point out what you think is the better alternative. the fact that your name is on your post conveys all the authority needed, and if you need to warn them of the technical consequences, warn them, maybe we'll find a way past that challenge, too. i don't think that kind of peripheral creativity will hurt tc or your goals and this community has no desire to thwart them, just to have fun and help people do what they want to, when possible.