I'd like to see the promotion tree reworked, but it doesn't NEED to be.
I'd also like to see them able to move through closed borders, but they don't NEED to
Ok, ok. We can do it in more steps. So let's ask this: what is the bare minimum we wish to see now?
1. Better survivability, without making them warriors or walls.
2. Better recon role, so they can still be useful after map revealing.
For 1, the most effective is retreating promotions. Having extra sight also helps, but more often than not, the path is blocked with a barb camp full of archers. If you want to explore what's behind you need to stand 2 or 3 turns under heavy ranged fire. The other threat is barb horseman.
Even without extra CS, scouts will be enhanced if they are given the chance to retreat. Other posibility is to have the hiding ability.
1a As suggested by G, 75% melee evasion. As it currently works, it means that unit has
75% of retreating BEFORE melee hits. But 25% of times, the horseman will crush our scout and he is still vulnerable to arrows.
1b This I offered in one of my promotion reworks:
100% of retreating from first hit. No matter if it is a horseman or a ranged attack, the scout will move backwards before he is hit, but only once per turn.
1c Hiding. The more I think about it, the more I like it. There are several ways of making this ability, but here is one: Scouts hide automatically when ending turn in rough terrain, scouts hide manually by fortifying. When hidden the unit cannot be seen unless it is adjacent or is seen by other scouts. When a non-scout unit, in its turn, reveals a hidden enemy scout, this unit loses movement for this turn and/or suffer damage.
For 2, the bare minimun is starting with
1 more sight, so they can do recon work better. With the Hide ability, the recon role is also improved. Explorers allowed to sail oceans is also good.
Movement needs to be addressed, and promotion branches aren't fully functional IMO, but this can be done later.