The Variax electric is on my to-buy list when I've got the dosh. Fantastic idea, and I've heard it used very effectively on stage.
I'm less convinced about the idea of the acoustic one. I've not played one yet (planning a trip to somewhere that sells them to see what they're like), but I'm not sure how well it'd work. Where the tone of an electric derives mostly from features (generally inadequacies!) of the pickups and the pickup location, there's so much variation in acoustic guitar bodies that it's difficult to see how it could be modelled accurately enough. Electrics only use a fairly narrow frequency band, where acoustics go all the way up. Plus the tone of an acoustic in an altered tuning also derives from the sympathetic resonance of the strings, and it doesn't seem to me like you'd get that when the strings aren't really detuned.
But I guess it depends on your needs. If you already own a Collings, a Lowden, a Benedetto and a top-of-the-range Ramirez classical, and you plan on using a mic for amplification on stage, you don't need it. But if you don't already have a bunch of good guitars and you're going to be playing on stage using a pickup for amplification (especially if that's as part of a band), maybe it'd be close enough for you, and it'll give you a lot more variety of sounds for the same money.
And significantly more convenient too. Re the keyboard thing, whilst none of them can compare to the sound of a grand piano or a pipe organ, the simple fact is that you can easily transport a keyboard to gigs, and fit it in your living room. You might only get 75% of the sound quality of the original, but if the original simply ain't an option then settle for second best.