> Because the brine is hyper-salty compared to ocean water and takes a while to mix back in, essentially creating a new ecosystem, brackish, where the outlets are.

How large would those brackish areas near the outlets be? It seems to be that would be a big problem in an enclosed bay, but much less so on a shore facing open ocean.

Could they run pipes out a few kilometers with small, regular holes (maybe some modification of oil pipeline technology) to spread the discharge out and mitigate the concentration problem?

Could they make the waste output less concentrated? Maybe by either running the desalination process less (would that also increase energy efficiency?) or by pre-mixing the waste with some un-desalinated intake water?

The pipe with many holes is one of the solutions used today it's just imperfect and requires a lot of pipe to make sure the waste output isn't too concentrated in a single area.