I've been debating this same thing for my current build. I really wanted to do road cranks and road RD but there really isn't a good triple option out there with the combo that I want. I'm running Shimano LX (MTB) 48/36/26 with a 11-34 cassette. Most of the time, I never use the 26/34 option but there are times when I'm tired and I just like to spin. Most of the road triples that I've looked at (Ultegra) are in the 52/39/30 range. If I were to go with that setup use an Ultegra FD and long reach RD, I think I could get away with an 11/32 but the chain would have to be crazy long to accommodate that.

With a compact double 50/34, I would lose that really low gear and I think that's something I would miss -- especially on those days I'm really tired.

So after some soul searching, I've decided to just stick to the MTB drivetrain and keep the same type of setup since this is what I ride now and I like the gearing. One can get XT level cranks. The difference in weight between LX and XT is ~300 grams for the weight weenies. The XT level cranks weigh about the same as the Ultegra triples ~650 g. The issue is that in the US, LX is about as good as you can get. I can get the XT cranks on ebay but they are shipped from the UK. I agree, it seems like component mfg. have forgotten about the triple setup.

If you're interested in the XT cranks, the p/n is FC-T780 Note the T. If you look for M, you'll get the 44T chainring. And you'll need the appropriate FD and that p/n is FD-T780 Again, note the T. The T is for Trekking and M is for MTB. If you do choose the wrong FD, it will still shift the chain, the shifts just aren't clean. There will be a slight hitch going from the small chainring to the middle ring. I made that mistake on my current bike. I've tuned it the best I can and can live with it.