Let me start with this may be a bit of an 11th hour suggestion.
I think it would be interesting (maybe as a game type option) to have all players start with owning all the equity (i.e. all the shares) of their company. This would then in turn tie into the debt system so that when your debt is more than what a current block of shares would sell for then a block is automatically sold to the bank (not owned by any player) and the money that is received is applied to your debt. When you have no more shares to sell in this fashion then the debt mechanism works as it currently does.
Example - opening share price is $5, I win the first auction with a bid of $6000, one block of my shares is sold to the bank at $5000 and my debt is now at $1000.
I think this would more closely simulate how equity markets are used by starting companies.
As a game mechanic the downside I see is what is there to keep a player from selling all their shares after they place their HQ and then vault to rank 4 or 5. There are the current mechanics that would make that risky, such as tanking your stock price or paying through the nose for the aluminium, glass, steel, or carbon for the upgrades and structures. However a few additional rules around selling to generate cash could be included:
1) You cannot sell until either the last HQ is placed or say 3 minutes have elapsed since you placed your HQ whichever is first.
2) There is a timer of say 10 - 30 sec between when you can sell your own shares.
3) There is a timer of say 30 - 60 sec between when you can upgrade your base.
I am less worried about black market shenanigans since there is already a timer there.
