I seem to recall something like this back during the OotA discussions; essentially coupling one terrain table with one encounter table. Perhaps it was you whose posts I read...?
Possibly! Ultimately, you may prefer a more mechanistic solution. But I don't think my suggestion is mutually exclusive by any means; actually, it may support some of the ideas you've presented.
Let me dig up what I did before....
https://www.icloud.com/numbers/000LUyAkAAFeENY3nQC8_13vQ#Underdark_Encounters
Chance of Random Encounters/Environments
Roll d20 (once per 4 hours, or twice/thrice per day, at DM discretion), making a roll on the "Encounter / Environment Features" table if check reaches target number described below:
20+ Sanctuary
18+ Frontier/Neutral Settlement
17+ Unexplored Wilds
15+ Hostile Wilds/Settlement
Encounter / Environment Features Table (d100)
1-50% 1x Encounter
51-56% 1x Encounter 1x Feature
57-61% 2x Encounter
62-71% 1x Feature (with +25% on roll)
72-81% 1x Feature (with +50% on roll)
82-86% 1x Encounter 1x Feature (with +50% on roll)
87-91% 2x Encounter 2x Feature (once with +25% and once with +50%)
92-96% Recurring Merchant
97-00% Weird Stuff
Encounter (d1000)
I used these guidelines in assembling Underdark encounter tables acc. to specific terrain types (e.g. Chasms, Dead Caves, Mines, Mushroom Forests, etc). Could be applied towards expanding Chult tables if one wanted.
1-500% Common monsters (50% chance)
501-800% Uncommon monsters (30% chance)
801-940% Rare monsters (14% chance)
941-1000% Very rare monsters (6% chance)
Environment Feature (d100)
I used these guidelines in assembling Underdark encounter tables acc. to specific terrain types (e.g. Chasms, Dead Caves, Mines, Mushroom Forests, etc). Could be applied towards expanding Chult tables if one wanted.
1-50% common (plants, flavor) (50% chance)
51-75 uncommon (hazards) (25% chance)
76-90 rare (hazards or wondrous) (15% chance)
91-99 very rare (wondrous) (9% chance)
100+ roll two more times on this table, with no bonuses on the two additional rolls (1%+ chance)
Reaction Table (2d6)
Use this when you're not sure how monsters would respond to PCs, or when you have two groups of monsters in same encounter to determine how they interact with one another. The DM can add up to +/-4 based on the type of monster or circumstances.
2-5 Hostile
6-8 Cautious/Indifferent
9-12 Friendly/Willing to trade
Natural Doubles
1's The monster takes hostile or violent action because of an outside influence. Perhaps the monster is charmed, rabid, insane, acting under compulsion from another creature that is holding its young hostage, etc. [Carl's suggestion for additional seed info: If the monster is intelligent, it may have specific information on the PCs or their motives, or may have been tracking the party with intent to mislead, deceive or ambush them. Possibly has set a trap for the PCs, and/or has magical item or psionic abilities that it plans to use against the party.]
2’s Something happened recently to make the monster angry and hostile to the world in general. Negotiation is unlikely to succeed unless it resolves the cause of this underlying anger.
3’s The monster would prefer to be aggressive toward the party, but something holds it in check. Perhaps it is acting under orders, has taken a vow, or is favorably disposed to one aspect of the PCs’ appearance despite hating the rest.
4’s The monster would be favorably inclined to the party except for one nagging detail. Perhaps it is prejudiced against one particular party member, or upset about a past action of the PCs.
5’s Something happened recently to make the monster happy and well-disposed to everyone it meets. Negotiation is likely to succeed unless the PCs seem inclined to take away the thing that is making the monster happy (a pile of treasure, a tasty human baby).
6’s The monster receives the party enthusiastically due to mistaken identity or a belief that they fulfill a prophesy. All will go well as long as the PCs continue to conform to the monster’s expectations.