I'm not sure Nike or Adidas or Reebok would have the grounds to sue. IPF's house, IPF's rules. If a manufacturer paid to be on the approval list and got taken off the list in the middle of the year, they might sue. But for a company like Nike, if the fee is $5,000 it's not worth the legal hassle, whereas it would be more than a drop in the bucket for someone like Dean Best.
Again, politics. Competitors can voice their opinions by moving onto other federations, but I kinda get the feeling that many competitors will buy what's approved if they don't already own approved gear.
Another question is how many competitors will be affected by this? Enough to make a change? Inzer, Titan and SBD have the lion's share of the market.