I define backcountry skiing as being more concerned with going nifty places than what you do along the way (ie the quality of the turns is not primary, and often is really bad). The winter version of backpacking or mountain bike touring, really.
The problem is that there is no definitive answer for this. Everything is a compromise, and it's tough to decide which compromise will be best for you without buying gear and trying it out. I'll give a run down on the major systems as I see them, and some thoughts on gear.
Caveat emptor, I'm in my second season of doing this, still have lots to figure out, and still suck at much of it. But man is it fun!
-These are all optimized for mountain skiing, that is, either going up fairly steeply or going down. Big hills, full skins, etc. The problem is that there is often a long, rolling approach to the big hills, and full skins and 4+ pound plastic boots are very slow at this sort of thing. This is what most people seem to be doing, but even if you do live close to big mountains, these setups can be a serious liability. On the other, being able to bust funky snow on big descents, rather than flail down with survival turns, has it's virtues.
-These are what Silvretta's were made for, going over the woods, glacier, and icefield to get to ice climbs and alpine routes. Some bindings have release setups, others don't. They'll go up fine, but turning in mountain boots will be a serious compromise. The sole is too stiff for good kick and glide, and the ankle too floppy for turns of any kind.
-By which I mean skis with a tip less than 100mm and a waist less then 70 (and often much less), with 3 pin or NNN-type system bindings, and heavy plastic/leather boots (or all leather). Skis like the Karhu XCD or Madshus Glitterind. Might be the best all-around answer, especially for making miles and taking the path of least resistance. Real good tele technicians can make turns down steep stuff and/or in less than perfect snow with this kind of gear, but I tried that and it will takes years of apprenticeship (ie flailing) to learn. Increasingly I think about getting a rig on the lighter end of this spectrum for trail touring.
XCD/Tele, new generation:
-Here we're talking low plastic boots, and skis like Karhu Guides and Fischer Boundless Crowns. Neither of these skis are made anymore, oddly enough. The fatter skis give more float in powder with a pack, have more mass and girth to drive through funky snow, but still are light (by AT standards), and have more camber than a modern AT or downhill ski. Plastic boots have a stiff enough sole to drive the big skis in un-ideal snow, and are made of softer plastic to maximize forward flex for touring. Binding are usually heavy 3 pins or 3 pin cables. Binding riser plates increase leverage for turning, and keep your binding up off hard snow.
I really think this last area is the ticket, the problem is that it's a very uncool market segment and thus suffers from a lack of product, and is the last area where the latest technology is applied. The latest generation of AT boots, for instance, are lighter than Excursions, have better forward flex, and are much stiffer and ski better when locked down. They're also very expensive. So, compromise is the order of the day.
I ski 185 Guides, with 15mm risers, Voile Mountaineer bindings, full width skins, and old blue two-buckle T2s. The skis and bindings I'm totally happy with. The boots are great going down, but have poor forward flex and are super heavy. I'd love to find some older brown T3s or T4s in my size (a bit lower and made of softer plastic, especially in the toungue), but they've become very coveted and hard to find.
I'm totally sold on waxless for multi-day touring with turns. In certain snow conditions (fresh, cold snow) using kick wax on waxless XCD or tele/AT skis is very effective, and you'll want it in your bag of tricks regardless. There are many conditions, however, where waxing is tough, and those are generally the conditions where waxless works well (ie warm snow, rough and refrozen snow). The other problem for multiday trips away from the wax iron is that getting kick wax off the skis when conditions change is a pain, and god help you trying to get klister off your skis once the snow goes down and things get cold.
For spring conditions, I don't bring wax, knowing that either waxless or full skins will work pretty well for any conditions. In deep winter, where light powder makes waxless largely ineffective, I iron some swix polar (the coldest hard wax) into the tail of my Guides. That makes a good base to apply green, blue, or extra blue as needed. I don't go warmer than that (messy), and I do NOT put kick wax into the waxless pattern. Impossible to get out without an iron, and you're setting yourself to have crazy snow-globbing issues on a multiday trip with various conditions.
Those are my thoughts. My skis are dialed, but I'm still looking for better boots. Which may not yet exist.
I'm very interested in hearing others thoughts.
Oh, and get all the avy education you can!