The only benefits I can see to doing this would be ones that would make things more difficult for your opponent, such as having a Burning World in play as well as a Lavapult or Volcanic Eruption on all 5 paths, or giving you more space for items/auras/traps. Note that this also limits the effectiveness of cards like Temporal.
Many items don't affect any path, such as the various 0 pp power providing items and things like Blood Orb and Tide Caller. Part of the "cost" of using these cards is taking up a space on one of your paths that now can't be used for path-affecting items or auras, as well as reducing the number of available spaces for other items/auras/traps.
I think providing one or more spaces in addition to the 5 available now would shift the game balance in an unnecessary and likely detrimental way.