Skysovereign, Consul Flagship

Oracle Text
Flying
Whenever Skysovereign, Consul Flagship enters the battlefield or attacks, it deals 3 damage to target creature or planeswalker an opponent controls.
Crew 3 (Tap any number of creatures you control with total power 3 or more: This Vehicle becomes an artifact creature until end of turn.)
Card Rulings
9/29/2017 Each Vehicle is printed with a power and toughness, but it’s not a creature. If it becomes a creature (most likely through its crew ability), it will have that power and toughness.
9/29/2017 If an effect causes a Vehicle to become an artifact creature with a specified power and toughness, that effect overwrites the Vehicle’s printed power and toughness.
9/29/2017 Vehicle is an artifact type, not a creature type. A Vehicle that’s crewed won’t normally have any creature type.
9/29/2017 Once a player announces that they are activating a crew ability, no player may take other actions until the ability has been paid for. Notably, players can’t try to stop the ability by changing a creature’s power or by removing or tapping a creature.
9/29/2017 Any untapped creature you control can be tapped to pay a crew cost, even one that just came under your control.
9/29/2017 You may tap more creatures than necessary to activate a crew ability.
9/29/2017 Creatures that crew a Vehicle aren’t attached to it or related in any other way. Effects that affect the Vehicle, such as by destroying it or giving it a +1/+1 counter, don’t affect the creatures that crewed it.
9/29/2017 Once a Vehicle becomes a creature, it behaves exactly like any other artifact creature. It can’t attack unless you’ve controlled it continuously since your turn began, it can block if it’s untapped, it can be tapped to pay a Vehicle’s crew cost, and so on.
9/29/2017 You may activate a crew ability of a Vehicle even if it’s already an artifact creature. Doing so has no effect on the Vehicle. It doesn’t change its power and toughness.
9/29/2017 For a Vehicle to be able to attack, it must be a creature as the declare attackers step begins, so the latest you can activate its crew ability to attack with it is during the beginning of combat step. For a Vehicle to be able to block, it must be a creature as the declare blockers step begins, so the latest you can activate its crew ability to block with it is during the declare attackers step. In either case, players may take actions after the crew ability resolves but before the Vehicle has been declared as an attacking or blocking creature.
9/29/2017 When a Vehicle becomes a creature, that doesn’t count as having a creature enter the battlefield. The permanent was already on the battlefield; it only changed its types. Abilities that trigger whenever a creature enters the battlefield won’t trigger.
9/29/2017 If a permanent becomes a copy of a Vehicle, the copy won’t be a creature, even if the Vehicle it’s copying has become an artifact creature.
Vehicles are so cool. A flavor homerun, synergizes with Fabricate, and powerful to boot. A 5-drop 6/5 with flying that Lightning Bolts on ETB and every time it attacks is insane. A weenie/token deck could easily make this work.
Note how it doesn't specify that you have to tap UNTAPPED creatures. You could tap an already tapped creature to turn on your Vehicles. This lets you get aggressive with your creatures, and have Vehicles ready to go for blocking. It can also give your fatties pseudo-haste, tapping them after you play them to turn on a Vehicle and attacking with it.
The next point of notice is the wording printed on the Crew mechanic, which reads: "Tap any number of creatures..."; again, not specifying untapped creatures. However, an oracle text search of "Tap any number" returns a number of cards which involve the tapping of creatures as an activation cost. But here's the thing, they all specify untapped creatures! Devout Invocation, Mossbridge Troll, even cards as old as Marshaling the Troops which don't specify "as written" have had their oracle text revised.
Bottom line is, Crew uses a precedent rulings text as the activation for an ability, which has specified that the "crewing" creatures be untapped. While it can be logically implied that the creatures be untapped in the first place (as is the case with Convoke) it would be nice if the reminder text was at least consistent with the precedent. But power creep has come so far that oracle text boxes are quickly becoming a fight between meaningful abilities and reminder text real estate.
@diegodeschain
Did some research, I was wrong.
If you have a card like Pressure Point, the target can be a tapped creature. Nothing will happen, but that creature is still a legal target. Same goes for a card like Sleep. The only necessary requirements to be affected by those cards are to be creatures, and whether they are untapped or not, the card still takes effect.
However, when you targeted a tapped creature with Pressure Point, that creature is not tapped. They were simply targeted by a spell. Since you can't tap a tapped creature, the spell did as much as it could. "Tapping" refers to the change between untapped and tapped. When you tap to pay a cost, that creature must actually go from untapped to tapped to pay that cost.
So with how Crew X is worded, you must have untapped creatures. I was very wrong. Sorry about that.
Still, the prospects are very exciting. You can tap a 3-power creature to attack with a 6-power flyer that turn, effectively doubling that creature's power, not to mention the free Lightning Bolt. With vigilance, you could attack with your creatures, then tap them on your opponent's turn to crew your Vehicles and block.
But if what you are saying is true, does that mean tapped creatures can no longer be legal targets for a tapping effect and untapped creatures are no longer legal targets from untapping effects? Does Refocus essentially read "Untap target tapped creature," whereby 'tapped' is a property of the target which if untrue on resolution causes the spell to fizzle?