The Pictish Confederacy

[Taranaich]

Would it be possible to give the Pictish Shamans the ability to call a Warpath like the Apachean Tribes? This could be a huge advantage for the Picts to not only have very much increased movement ability; but also to supplement their numbers very quickly with "horde" type troops that the Warleader could summon to him at little to no cost in raising new troops.

You'd better believe it. We see such a thing in "Beyond the Black River" where Jhebbal-Sag pulls together a whole horde of tribes to invade the Westermarck, so it's a no-brainer to implement it for the Picts. Indeed, this is one of the biggest problems the Aquilonia player faces, because it can come out of nowhere and overwhelm your forces unless you take out the Shamans preemptively (a mechanic related to my overhaul of the religious aspect into something else).

Also, using the Apachean Tribes, you could allow the Picts to gather technology that would allow them to later build structures that allow them cavalry even...just like in Howard's history. I don't know how you would change the muskets to just weapons...like I said, I know nothing of computers; but I thought perhaps it is possible.

In addition to the dreaded Pictish Reforms - a dynamic which requires a couple of conditions - there are a few of those technology-stealing Pictish units. Pictish Warriors are most common along the south & south-western frontier, having stolen, traded or found swords and mail armour and putting them to use. The Reforms would bring Pictish Swordsmen, Pictish Spearmen and Pictish Cavalry, with the present skirmishers & light infantry rounding up the deadly fighting machine. Plus the magic aid the Shamans bring like beasties and offensive/defensive sorcery.

I was thinking that maybe the Shark tribe, (you mostly thought of it already). Giving the sharks a primitive navy, starting them off with canoe's or a bigger war canoe (like the polynesians) and then maybe when the revolution starts to progress, give the picts (Sharks) bigger and better naval ships?

Quite possibly. The Picts never become the fully-fledged navy that they were in Thurian times, but they do indeed have polynesian-style war canoes, some rivaling the Black Corsair's galleys in length. The Sharks will have fast attack canoes, the Otters larger war canoes, and the Alligators big 20-footers. The Pictish reforms will allow the creation of big double-hulled waʻa kaulua-types like the Hokule'a (which I imagine is the type of craft the Thurian Picts used to travel across the world)