1) your first point seems to be mixing quality ("niche product") with the production/processing facilitise in Chile already. I am not really sure why this is the case.
2) It is not a matter of competing with the existing Chilean production. If the market is growing, then the question is can you continue to expand existing facilities and if so, by how much? Do you continue to expand existing facilities in the same place or look to other locations to diversify. The locations for this species are limited globally.
3) I doubt this is being pushed 100% by the government as an avenue to increase industry but rather being pushed by industry to what they see as a favourable governing party at the moment. Considering that the legislation requires studies and impact assessment, it gives the companies time to complete such works, and by the time any real investment comes up it will be election time and they will see by then how things have progressed and which party is expected to win by then. They won't have to commit to investment until after next election.
4) The risk is the Chilean government. If another party comes in and wants to limit expansion, or reduce industry due to the inherent risks with farmed fishing. If so, the companies may want to have other places that they can easily swap to at the time, possibly just the farming aspect, and keep processing in Chile, or move/parallel operations in Argentina. As a business its a risk mitigation exercise for them to know if they have opportunity to operate in Argentina. Whether they choose to or not is a separate issue.
5) As mentioned in 3) they will have time until investment is needed to see how the economy and politics goes. I would include in this that the Venezuelan situation will be interesting as well as its implications for Latin America. It is still the same governing party, but if under pressure from the US things were to change there and the quality of life and economy improves, it will be a point of interest in why things have gone so slow here. It will probably provide more support for the right than the left in Argentina.