In general, I'd love to see both more cross-discipline results for the tech columns, and cross-column dependencies. The cross-tree benefits would simply be fun, and the cross-column dependencies should help prevent the rush-to-the-top researching that happens currently. Here are some quick ideas (probably not all good):
Bonuses from other paths in the tree could be things like:
1. war paint - a battle item gained directly from diplomacy (described below)
1. researching enchantment and a specific spellbook might make an additional element-specific item available
1. adventure resource discovery requires some ruin delving after a certain level. Not only prevents straight to the top, but adds a level of risk to searching out the resources. (Also please adopt more civ-like view of these - only seen by those who have researched high enough, but not just single spawns inside your domain)
2. a certain minimum armor level for a given weapon level (no legendary weapons with no armor at all), and vice versa - because that's just weird.
1. make the more legendary equipment in Warfare require civ production, and at least basic magical equipment researched.
2. at least basic diplomacy before allowing larger squads (discoveries in organization & leadership)
More specific ideas
I don't know if the capabilities for these sorts of things are built in or not, but I'd love to see things like:
spell: arcane bolt (known at startup, only available to sovereign)
damage: int/4 per bolt
number of bolts: 1 + # of shards (or level?)
cost: 1 + floor(bolts / 2) mana (this comes out to 1 mana per INT/2 damage, which seems fair)
Designed to give a somewhat-scaled offense to the sovereign that allows them some offense right from the beginning. Multiple bolts could be assigned to the same or different opponents (fire all at once or a quick stream).
auxiliary (additional to normal weapon) attack item: lance
required for selection: horse equiped
adds special ability: charge attack: 2.5 damage, must have moved at least 2 spaces, available 1x per combat
required for availability: mounted warfare (or something further?)
miscellaneous item: war paint
adds special ability: berserk attack: 1/combat attack for 2x damage, defense is halved for retaliation (or until next turn?)
required for availability: something in diplomacy (greater psychological understanding)