The only issue I can foresee, and the only one I see now, is that if you are interested in any sort of touring, you're virtually screwed if you find yourself in need of a new tire or a new tube for that matter!!!!
Out of four local bike shops I called one had 27s in stock, (called a few weeks ago) but not a touring tire,..sorry but I'm not interested in "making do" with a road racing tread when I'd prefer and do better with a touring tread for grit, gravel, dirt AND pavement...
I actually just bought a set of Conti Tour Ride 27s,.. I haven't switched and I probably won't till next spring/summer when I start a "little" bit of short touring...
If you're not touring,.. stick with 27s,.. but that's just my opinion. There aren't vast amounts of 27 tires to choose from, but they're out there, not readily available at your local shop either (unless your local shop specializes in vintage bikes).
Ride on!