Brightline managed to deliver their Florida line pretty much on time and on budget.

The only real challenging part of the route is going to be pass out of the inland empire where the I-15 grade is a really steep. The rest of the project is pretty straightforward, with rights of way already in place and very few expensive and complex grade crossings. They picked this city pair and route very carefully to have an excellent chance to succeed both on construction simplicity and ridership. I'm not sure they will actually open in time for the 2028 Olympics, but I wouldn't bet against 2029 operations.

As for high speed, it won't be able to sustain true high speed rail velocity across the whole route (150mph / 250 kph), but it will be much faster than driving and there will be long stretches that are very high speed.