The general form of #18xx legal track-tile upgrades is simple: any strict superset.
Worth challenging? How about:
( @18xx )
Which worked well (I'm hoping to revisit this with 1836).
I found having some external structure was necessary. I did it there through map-shape & off-boards which gave incentives & competing options. So: still organic & collusive...but not entirely laissez faire.
Another project (not mine) gives a revenue bonus for every station in a city other than the active company's -- which works & gives curious incentives, but is fiddly. I've also been tempted by stations not blocking, but cities paying $0 if run through without the active company's station (full revenue if the terminus).
Option 1 sounds a bit take-that-y. I upgrade the cities that I am not in simply to punish whoever is there. Upgrades should cost to balance?
Option 2 weaponises tokens in a new way; I hurt your future revenue but at the cost of using my limited tokens. End result no one goes to Chicago/New York/any other high revenue location... because everyone knows it will end up blocked at greens and therefore mid-revenue routes get more developed?
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