I’m not convinced with older framesets built up with ultra modern groupsets and I don’t think the market is either as they seem difficult to sell.
My perfect bike would be a 1980’s 753 frame built up with an older square taper Super Record EPS 10 Speed groupset with modern Brifters, a bit like the new Ti rep but more authentic.
I can see where you're coming from and as a rule I'm similar with keeping old / collectable stuff original; which is why really I'm looking for something a bit tatty that's already lost its originality / collectable value. I certainly wouldn't corrupt anything genuinely rare or as nice as the Corsa in my previous link with modern groupset; although if buying a complete bike I'd keep all the components removed and look to keep mods reversible (unless it was that tatty it warranted a refinish).. hence my search for frames that will take recessed brake nuts to avoid having to drill the frame. I'm also aware that the dropouts will need a bit of persuasion to fit a modern 130mm hub, however don't see this as a major issue since on later frames it amounts to all of 4mm.
I hear what you're saying with the campag groupset; certainly a bit more sympathetic than a complete modern groupset. That said modern campag stuff seems to retain a much more classic aesthetic than the Jap components and I'm guessing there are fewer problems with shifter compatability / gear index spacing on the Italian stuff?
In my head I think a modern groupset could look really good on the right frame and have seen a few nice examples, although it's no surprise that such stuff doesn't sell well as you've narrowed your target market enormously - shutting out the originality-freaks who might otherwise have apprecaited the frame as well as the modern afficiandos who'd scoff at steel in favour of CFRP...