I don't remember if "fun" was specifically discussed, but the discussions were more focused on what users would do and see, very much in keeping with your second paragraph.
The product manager was also asked to consider the exercise from a competitive perspective. What could be done to differentiate a new site from an existing, popular site? is the strategy to be simplere and easier? To cater to power users running into limitations of the existing site? And so on.
I develop s/w in an R&D environment. My users are very specific about how they use information, but know almost nothing about s/w development. Likewise I know little of their specific domain, but can develop whatever tools they need. While I can craft and code algorithms that should dazzle them, if it doesn't solve their problem they won't use it. For me, design has to account for the users' experience as well as developing clever and efficient algorithms to solve problems.
I really love the original question, Reg. It was fun.
There's not really a good digital equilvalent to this, but that's the tricky thing about monopoly: the things that set it apart from other games are the hardest to transfer to a digital analogue.
This reminds me of the ongoing quest to make a popular online version of Cosmic Encounter. I grew up playing the paper version with every expansion. There were so many aliens to be (and we frequently played with two/person) that the dynamic was different every game. But to add a new power to the digital version can require a whole new set of rules, and so they always fall startlingly short. [as a brief example, the Filch power, when coupled with it's power card, allowed you to cheat by secretly taking cards from the discard pile and whatnot until you were caught - this is nearly impossible to accurately mimic digitally]
When I'm only doing average or not so well as I want to let on I make sure I have my 1000s on the top of a large stack. When I'm clearly leading I spread all my money into individual stacks so that people can clearly see that I'm far in the lead. The same goes for properties. Especially when I have stuff built on them. Anything with the most value is up in people's faces unless I'm slightly behind the curve where I obfuscate what I have to not seem a threat. (Games of monopoly often turn into horse trading in the late stages.)
Translating that online would be hard. Fun but hard.
What makes the game fun? Part of it is the interaction between players, laughing, joking, scheming, and posturing. How do you bring that to a game played over the net? Is text chat sufficient, or can you easily do voice? What do you display to the players? Certainly part of the board needs to be displayed. When I play, I like to see what people have for properties and money. Will I be able to see that Alice has a stack of $500 bills or that Bob has nothing larger than a $50?
The original question is a very cool thought experiment, imho. My initial reaction was that to design this, I'd want to sit and play some games of Monopoly to see what to include and to see what the game is really all about. I've played hundreds of games of Monopoly, but that's not the same as designing a fun game to play over the net. Running through this little thought experiment helps raise many questions about how the game will work. Does each player have a complete client, or is this a server based system (or is it somewhere in between)? How do you handle dice rolls? How quickly can people start a game?
You need to know what you're going to create before you start applying tools to create it.