Are the disqualifications justified with the current regulations?
In Section 1B, Appendix 4 of the Badminton World Federation (BWF - the international governing body for the sport of badminton) Handbook is the Players' Code Of Conduct. Regulation 4 lists the "Players' On-Site Offences."
Regulation 4.5 states, "Failure to use best efforts" whose description is, "Not using one’s best efforts to win a match." The BWF is also charging the players in violation of Regulation 4.16 which states, "Unsportsmanlike conduct" whose description is, "Conducting oneself in a manner that is clearly abusive or detrimental to the sport."
Regulation 2.3 of the Players' Code Of Conduct state:
Any player who commits any offence defined in Regulations 3 to 5 shall
be deemed to have breached this Code. Breaches of the Code constitute
the basis for disciplinary action against the player.
Therefore, if judges determined that a player was "not using one’s best efforts to win a match," then the disqualifications (and subsequent disciplinary actions) are justified.
Has something like this happened (in this scale that is) in badminton, or any other sport, before?
In London during the 2012 Olympics, Japanese soccer coach Norio Sasaki instructed his players not to score to maintain a 0-0 tie. A tie means their team would stay in Cardiff, rather than going to Glasgow, for the quarterfinal. However, no disciplinary action will be made by FIFA.
What implications will this event most likely have on the sport, or the Olympic games as a whole?
The "round-robin" system was set up for competitive balance. In the old system, a country could win gold and silver medals by winning all their games. In the new system, the intent was to prevent such by making teams with the most wins eliminate one another before the finals.
The Chinese tried to take advantage by losing so they didn't have to eliminate their compatriots. On the other hand, South Korea deliberately tried to lose so they could play easier opponents.
I would imagine the BWF will change their system to prevent anything similar from happening in the future.....perhaps single-elimination games?
As for the Olympic games, that's a work in progress. There has already been much controversy surrounding these games, and this situation helps none. However, as big as the Olympics are, there will be a new crop of players training to compete for their country in 2016.