Hello and thanks for your input.
Well, I missed that series. But I am big fan of Doctor Who. Sadly, mechanics used there are not of much use for my project. As Doctor himself said, "time is big ball of wibbly-wobly timey-wimey stuff". While there are some good pointers, it is not entirely applicable to my case.
Also, I want some maleability to be possible - permanent changes are not exactly I am aiming for. So bit of flexibility, and possibility to repair changed event is needed.
Still struggling if to use "timewaves" (like in Achron game) that propagate changes at certain periods (not sure how long should they be), or "reality factor" (percentage that determines, how probable each variant of event is) that would be instantly recalculated when players made change at that time-zone and propagate to "future" versions of area.
To your points.
Ad 1: I agree, that long would be better. Keeping tabs of all shadows of "past" players meddling would be too cumbersome to maintain. Also agree of some kind of consequence for players - depending of how "unreal" their "home reality" would become, they should be given some penalties (experience lost, becoming more transparent and less able to affect past events, etc). Still WIP.
Ad 2 and 3) Good point. Version with too low "reality" should become unacessible to all, until somebody manage to revert it to safe threshold (should it be group effort, or allow some events be soloable?). This could allow to spin-up areas of "unreal" versions of areas only when needed (or keep separate version up for those, who have it as their "home-time"; or not - time-orphans fighting to reestablish their home-time? Hmm.).
Ad 4 and 5) So, I was thinking about starting with 10 mutable zones (with 5-10 key points max each), connected with "immutable" passages. Focusing more on temporal aspect, while keeping bit of variability. That makes 310 individual area versions for minimum set, while rising to 15.350 if aiming for upper set (whoa!), if I am counting right. This with only two change options in each period. And I was thinking about to allow 3 options at certain times... Hmm.
Example:
Lets have zone, called Alpha, that is (to make it simple) in its original state grassy plain with small river, and grazing animals.
Local Conflict: Natural preserve VS Futuristic city VS Alien colony
Point 1) Year 0
Original state.
Changes: Place measuring probes VS Destroy them (no versions needed here yet)
Point 2) Year 100
Version 1: No probes - same as original (maybe different animals), no further changes in future versions
Version 2: Probes successfully deployed - first settlers arrived
Changes: Place city capstone VS Destroy it
Point 3) Year 200
Version 1: inherited from Y0
Version 2a: Capstone placed - initial construction of city commenced
Changes: Help construction VS Sabotage construction
Version 2b: same as v1
Point 4) Year 500
Version 1, 2b: Aliens landed and are building colony
Changes: Attack aliens VS Help aliens
Version 2aA) City constructed
Changes: Modernize city VS Sabotage
Version 2aB) City in ruins
Changes: Rebuild city VS Destroy city
Point 5) Year 1000
Version 1.2bA) Natural preserve established
Version 1.2bB) Alien colony alive - home-time for Alien Sympathizers faction
Version 2aAa) Futuristic city alive - home-time for Futurist faction
Version 2aAb) Natural preserve saved (in fact same version as 1.2bA)
Version 2aBa) Futuristic city saved (same as 2aAa)
Version 2aBb) Natural preserve saved - home-time for Nature First faction, otherwise same as version 1.2bA
No further manipulations in this point (save for future game expansion, of course)
This is of course simplified example, not taking into account changes via NPC dialogs (like in P3.V2a: Talk with founder to keep capstone at original place, or move to other river bank - would change future city design OR City Hall placement; etc), assassination vs saving of important NPC, etc.