I like your de-combine and Rehab Center ideas.

Just to clarify the Brain Storming...

My assumption is that in PvP mode you CANT "take" anything from the other player (because of blockchain, ownership of the NFTs, Active Keys and such) you can only "Mess with" the other players City like unloading a building, right? BTW I like the idea of messing with another City. Keeps you on your toes and forces you to check up on your City regularly.

So..

How about an "opt-in" where you "enlist" (Active Key Transfer cards to @dCity) your hackers or soldiers (or whatever cards makes sense) into the PvP game to accomplish some task(s). Then you could use your Soldiers to attack another City that has a "Standing Army" of enlisted soldiers that they also opted-in to the PvP game. Then these cards ARE at RISK of being won or lost.

This way you could "attack" another player who also opted-in and actually WIN his cards or lose your cards to him.
Of course the "attack" would have to have some sort of limits or random chance of win/lose placed on it to keep the BIG players from stomping the little ones.

You could also have groups/things like the "United Nations" that you could join where you had to "enlist" your soldiers and maybe a Military Complex and pay SIM which gets burned or added to the rewards pool. This "Group" would give you some protection from attacks and less risk of loss. These groups could also be governed by the group "members" and directed to Attack the "other side", kinda like the voting we do now for taxes and rewards.

So we could have a World War of sorts!

Maybe to start a World War all the "Members" have to PAY a (war costs) BIG CHUNK of SIM and that SIM is given to the members of the "Winning Team" along with some or all of the cards.

Also their should be a cost in SIM for any of these PvP actions. That SIM gets burned or added to the reward pool.

(pinging @gerber @scriptioner to read my comment.)