It looks to me like they come as a set with customisations. You choose your character, select their moves and equipment, and save that set-up. There is nothing immediately apparent that would warrant their exclusion.
Custom character battles should be about everything listed here:
http://www.smashbros.com/en-uk/howto/entry2.html
I feel like this is a starting point that should be easy enough to get on board with.
The logistical issues in question have to do with the availability of equipment on each console. I highly suspect that it will not be feasible on the Wii U.
Fortunately for the 3DS, that is not an issue. I only have a small problem with them, and that is they are not a zero-sum item. There are drawbacks to equipping them, sure, but you could equip things like....
+180 Power, -90 Speed
+180 Speed, -90 Power
What exactly does this add to the game? The stats on them are arbitrary, each time you get them they will have different stats. Players will be forced to farm equipment with the best stats to remain competitive.
My mario has the two equipment listed above, your Mario has...
+90 power, -45 speed
+90 speed, -45 power
I am literally playing a better character, creating what I would consider to be a slightly unfair advantage in my favor. Yes, I know, I've heard skill vs. gear for years while playing MMOs, but the fact of the matter is those stats will make a difference. If they didn't make a difference, what was the point of including them at all?
This would be similar to getting a competitive pokemon team in older games without cheats.
You have to:
Capture your desired pokemon.
Check it's stats, if it doesn't have the correct starting stats, you have to get a new one. (Six stats, values range from 0-31, I believe.)
Check its nature, if it doesn't have the correct nature, you have to get a new one. (25 natures)
EV train it (This involves only letting your pokemon killing certain pokemon until you've maxed out your desired values, takes hundreds of kills)
After that, you can train it to lvl 100. It takes months to get a competitive pokemon team without using exploits.
I don't expect the equipment from smash to be this involved, I'm just illustrating the point that if it is not moderately easy to obtain the best equipment in the game, it will probably not be viable for 3DS.