How many AI opponents appear? And do they work persistently, remembering if you undercut or push them near bankruptcy?
The AI is more passive than aggressive. TC:NY is about building up the whole of Manhattan. If you had to constantly worry about the businesses you set up six hours ago, you'd never get past TriBeCa which is only the second district in the game! The AI generally takes up the slack, helping you in that aim. That's not to say that it won't get in your way every now and then, forcing you to rethink your strategy.

How do you earn Landmark Bonds and how can these items affect your gameplay?
Landmark Bonds are awarded for reaching certain Milestones in the game or by completing Prize Opportunities - tasks scattered throughout the game with rewards such as new businesses, new upgrades, more Upgrade Credits and Landmark Bonds.

Landmarks have a massive impact on the local area for tourism, and some of them are real money making behemoths; well worth building up, and they really help define the Manhattan skyline.

Do you have plans for multiplayer options in this or future editions of the Tycoon City franchise? How might they work?
With the sheer amount of data that would need to be coordinated, keeping the 60,000 people synchronised across all machines, it would be a task and a half.

It would be a nice addition though, and from a gameplay standpoint there wouldn't be too much to design. Just put everyone into the same world and let them build away, creating a joint Manhattan.

Competition would come naturally, with each player trying to muscle in on the others' empires. Could be great fun!