That isn't portable anyway—small reality check...
I type in Czech a lot. We have 14 extra letters (latin letters with diacritic marks, actually... but it's not like it makes a huge difference, dead keys are kinda annoying). You know, size matters. Add proper quotes and other typographic symbols. Alright, let's add ANSI symbols used in system administration and software development, that's about 14 symbols. Now, what about embedded navigation cluster? Another 10 keys. How do you cram all of this on ~30 keys avoiding stuff like Emacs pinkies?
Small reality check—it definitely is portable. Just because you're ignorant about this doesn't mean you can tell me that what I've been doing almost daily is impossible (this isn't some hypothetical I randomly came up with). 
Besides that I wasn't just talking about the home row (which I use primarily for navigation; I don't cram everything there if that's what you were getting at), and I never mentioned other typographic symbols (total strawman basically). But yeah, I can and do do that too. You want all that on the keyboard? It's easy.
If you don't like dead keys.. well I can't help you. They are very useful. I have custom altgr mappings as well (including the num row). Proper quotes are easy to add. 30 keys is absolutely nothing for an altgr layer with dead keys. Even if you only used 20 (which is a lot less than what you could do) keys for symbols (and no dead keys), that's still 40 symbols with altgr and shift altgr. With just a couple of dead keys you'll get that same amount. Of course they wouldn't all be extremely easy to reach if you used more, but that wasn't even what I was talking about. It's easy enough to move just a few keys (ex: }, |, &, [, %, etc.) to easier reach spots. That's what I meant.
As for portability, I carry this around with me and have used it on many other people's computers (I only have encountered Windows, but I think I could do most of the same stuff on another computer running linux as well). Sure you may encounter problems at some point, but how is portability relevant to what I said either?
I have to agree with Linkbane about your other comment.
Yeah, I'm ignorant... user of an ergodox with Colemak customized to fit 76 keys. How ironic. I've had to deal with issues mentioned above. The 3rd/4th layer is already occupied by typographic and national-alphabet symbols. Dead keys break typing flow, considering how common diacritic marks are /in Slavonic languages. Even this is a problem on standard layout, because AltGr is only on one side and hard to reach on some keyboards (especially winkeyless). And with another layer, it gets only worse. Dual-mode modifiers would help, but they're PITA to deal with.
However, I have no problem carrying an ergodox/typematrix with me or switching between different physical layouts.
I said you were ignorant because you said doing what I suggested isn't portable. It wasn't an insult. I'm not even sure how anything you're saying now relates to anything I said. As for altgr being hard to reach, a wide mod (shifting right hand over one key) can help. You can also just remap altgr (not sure if that is possible portably, but it probably is). I'm not sure exactly what problems you're having with your layout.. it seems that you already have all the symbols you need mapped.. if so, what is the problem? I think you're addressing something that I didn't say.
I don't know what you want or are doing, but my original suggestion works fine for me.
Again: four layers might be enough for an English-speaking American (yay stereotypes!) outside academia or someone like that, but if you need to use diacritic marks or extra symbols all the time, it's a completely different story. That means another layer (like in case of DreymaR's mods or Neo). Last time I checked, it was PITA to implement on Mac OS X, and dealing with RDC and SSH was even worse.
In the end, it's just easier to bring some Teensy-based hardware... which is e.g. the ergodox—with plenty of (symmetric) modifiers, layers and macros.
Too bad I haven't had time to reupload stuff I deleted with my wiki and GitHub account.
Extra symbols/marks are only a PITA if you aren't willing to have dead keys ar add more layers. I will admit that I hardly ever use diacritical marks, so dead keys don't really annoy me.
Right now I'm using 5 layers on linux and windows and could easily add more. It isn't exactly hard to do. Might take a few hours, but then you're done. In my situation, I'm convinced a software solution is much better. I just don't have the space to lug around a keyboard or ergodox all the time. I'll probably look into them at some point (or maybe an arduino), but right now I'd only use a hardware solution out of necessity (which hasn't been a problem so far).
As for OS X, I honestly try to stay as far away from it as possible (xD), but if xmodmap works on it (I think it should but have not tested...), then it should be relatively easy to have 5-6 layers portably (as in just load a file with mappings from terminal and then restart to clear them or load back to qwerty mappings when done).
I mean.. ergodox is an impressive hardware solution (is 9 layers the max?), but I think you're overestimating the difficulty of doing this without one. I will admit it's probably a lot easier to do with an ergodox and not have to worry about this stuff, but then you do have to carry it around everywhere.
