Obviously our knowledge of just how flexible law-making will be is dependent partially on our knowledge of the contract system. Furthermore, it's one thing to conceive of a fairly robust contract system enabling players to finagle all the minutia; however, that may come at the cost of a system accessible to players and not overly complicated.
With that disclaimer out of the way, I would not like to see an overly simple system. ArcheAge is a nice example. The game's court system is simplistic: a player appears in court, an NPC adjudicates, and a jury of players deliberate and vote on the verdict. The issues are: (1) a limited number of sentences (e.g. guilty or not guilty), (2) no weight of evidence (there is no way to produce evidence), (3) the lack of seriousness among jurors.
Addressing these in reverse order, many of the jurors do not take the court system seriously. I would venture to guess it's because there's little at stake for the players involved. Also, most criminals are trying to up their infamy enough to become a pirate; so, there's even added incentive to draw a guilty verdict.
Jurors probably do not take it that seriously because the system is fundamentally based on the word of mouth of the players, and, given that any accusation can be made without empirical support, why hold the court to a standard of proof? Indeed, there can't possibly be such a standard.
Finally, there are really only two sentences: guilty or not guilty. The severity of the punishment is directly proportional to the type of crime multiplied by the number of times committed by the criminal. This actually isn't an illegitimate system.
The United States penal code has fluctuated between two points: strict sentencing and open sentencing (my non-technical terms). The former is much like the ArcheAge system. Judges consult what is essentially a chart, find the appropriate crime, and track the recommended or prescribed punishment based on the severity of the crime. The latter keeps the chart but allows judges to make changes to the severity of the sentence based on extenuating circumstances. For instance, there are cases involving thieves who, admitting to the theft, obviously committed the act due to a horrendous family situation or the driving force of poverty and starvation (think Jean Valjean).
So, CoE's legal system will likely fall somewhere along this spectrum. Naturally, the former model is the easiest to implement, but it is certainly less intriguing. The latter is interesting, but it is more difficult to implement.
Given CoE drifts towards the latter, and I think it is highly likely, I would like to see a lot of things mentioned in the above posts. Assuming that contracts will form the basis of the legal system, then a contract, or some version of one, will likely be basal to someone's being accused of a crime. Since formal accusation and trial is therefore legitimized by a document, that document can be voided by the judge in possession of that document at any time. So, fulfilling a Trial by Combat or some other interesting condition should be entirely feasible even if not included as a mechanic in the game. Likewise, this implies that the trial system can be tampered with if the wrong hands (with a skillful-enough use of the pen) gain access to the right documents.
Assuming that this level of complexity is instituted, I think we'll avoid issues (1), (2), and (3) taken above. The legal system might still not be taken seriously, but it wouldn't be taken seriously, presumably, in the right. Players might attempt to exploit it, find loopholes, or disrupt the legal process, but given the proper tools are implemented, those actions can be countered; thus, it presents an interesting puzzle and challenge for players.
My greatest hope (and greatest fear) is that, though the legal system (I'm focusing moreso on the court system here) might be a complex aspect of the game, it is an essential and worthwhile one. Essential insofar as nearly all players will have to interact with it at some point. Worthwhile insofar as those players who choose to play as lawyers/attorneys/barristers, legal scribes, and judges are able to sustain their characters given that style of play and are appropriately rewarded for it.