This is all getting a bit crazy. Let's step back a bit. Here's my take:
1.) Should scouts be able to attack or not. My vote is no, they should not. This allows us to give them a higher CS without risking their utility.
2.) Should scouts have a % chance to avoid melee attacks? Yes, 75%. This prevents scouts from being reliable defenders.
3.) Should scouts start with one extra sight? Yes. This makes scouts immediately useful and they retain this utility until explorers arrive.
4.) Should scout movement base/promotions remain the same? Yes. The current promotions are useful and functional.
5.) Should explorers be able to embark across oceans immediately? Yes. This gives them a niche (and will boost Brazil's units too).
So, Scouts will become hardier (increase CS to 12) but much more skittish, and will be the best 'scouts' until explorers arrive. Explorers will be able to sail across oceans earlier (if we move them back a tech). Zeppelins can fly over anything. Paratroopers/XCOM can drop in and get behind-enemy-lines bonuses.
This seems balanced to me.
G
1.)
Definitely yes. I find scouts invaluable against barbarians in the early game, and without the ability to attack they'll be helpless against ranged units, barbarian or not. Pocatello's pathfinders will also take a hit under this, making their additional combat strength relatively useless. I find the increase in combat strength by era to be a really interesting solution for making them stronger, although it would be strange for it to only affect scouts.
2.)
Yes, 50%-25%, along with % increase to CS on defense, but without the ability to fortify. To me scouts shouldn't be effective at holding land, but rather always on the move. This would allow them to be effective during war without needing to increase their CS significantly. Also, their chance of surviving an attack won't be so polarizing as unscathed or complete defeat.
3.)
Yes, completely agree.
4.) I don't mind either way, but I like
@ElliotS's proposal to have Trailblazer simply provide more movement. If sticking with the current promotion line, I would like to see the zeppelin have double movement over coasts and/or hills in lieu of their inability to use roads/railroads.
5.)
Yes, agree again, but I think their tech level is fine. They'll complement Caravels nicely.
Outside of these, I think allowing scouts and explorers to have the submarine's invisibility promotion would fit their role extremely well, and complement either opinion regarding the first two points. Defense won't be much of an issue as they won't be targeted as often, and they'll be able to infiltrate enemy territory more reliably. AI use may be an issue though.
I'd also love for scouts to be able to pass through territory without open borders, this way I won't have to worry about them being stranded for a few thousand years.