Point taken. The existing right of way is straight enought for most of the distance to allow speeds up to this amount. The tracks just need relocation, as I have said before: About 25 feet straight up. This will eliminate all the road crossing and trespasser issue at one swoop. Make it enough higher over Bay St. Louis and Biloxi Bay, and eliminate the drawbridges. Think of a time more on the order of 90 minutes to allow for stops and some slower running into the city centers at the ends. This should still be fast enough to capture quite a bit of traffic, particularly if there was a western extension to a point slightly further west, say like Houston and San Antonio.
I would think that distance is one of the few where a 220 MPH train could make trips practical that simply would not be any approximation of practical by any other mode of transportation. A 220 MPH train covering 145 miles could make the trip in about an hour each way, which is viable for a daily commute. There's no way an airplane or an automobile is likely to be remotely time competitive with that.
Mobile - New Orleans are really too close together for real high speed service. They are only 145 miles apart.
Lafayette, LA to New Orleans via Baton Rouge is about 135 highway miles, similar to the Mobile to New Orleans distance. So Lafayette to New Orleans is another potential high speed commuter rail route.
Getting from Lafayette to Houston is more like 215 highway miles, which is harder to make work as a high speed commuter rail route at 220 MPH. On the other hand, building a HSR line from Lafayette to Houston might allow people in Lake Charles and Beaumont to commute to Lafayette and Houston.
Mobile to Montgomery is about 170 highway miles, which probably needs to be somewhat faster than 220 MPH to be a reasonable commute, unless you're just focused on allowing people in the small towns between them to commute to both.
Montgomery to Altanta is about 160 highway miles.
Atlanta to Greenville, SC is about 145 highway miles.
Greenville to Charlotte, NC is about 100 highway miles.
Charlotte to Greensboro, NC is about 90 highway miles.
Greensboro to Durham, NC is about 50 highway miles.
Durham to Richmond, VA is about 150 highway miles.
Richmond to Washington, DC is about 100 highway miles.
It's probably possible to build HSR all the way from DC to Houston if your goal is to make every mile of high speed track be both a viable route for commuting into a major city from various small towns, as well as a part of a viable long distance intercity route. In many cases, it can also be practical to live in the downtown of a major city and commute to an adjacent major city.
It may very well be the case that when some of these routes are first opened, the major city to major city time needs to be closer to 90 minutes than 60. Route 128 to Back Bay on Amtrak is about 10-11 minutes now, as is New Carrollton to DC. And neither 128 nor New Carrollton is far enough out from the city to be the point where the 220 MPH track will start, if the 220 MPH track is not built in a tunnel under the suburbs. If you're spending 15-20 minutes on each end of the route traveling along a slow right of way through the city, that's 30-40 minutes when you count both cities, and only leaves 20-30 minutes for traveling on the 220 MPH+ track if the trip is supposed to be completed in under 60 minutes; 30 minutes at 220 MPH only covers 110 miles.
On the other hand, if HSR can be built through tunnels through mountains, why not HSR through tunnels 100-200 feet under the surface through the suburbs?
And why limit speeds to 220 MPH in the long run?
With conventional speed routes, we often see studies of both what it would cost to achieve 79 MPH and what the running times would be, and also costs and running times for 59 MPH or 110 MPH. I think it would make a lot of sense for high speed commuter rail studies to look at the costs and benefits of the tunnel through the suburbs option, and at the potential benefits of 300 MPH operation once that equipment is developed (and what can be done relatively inexpensively during initial construction to save money upgrading to 300 MPH later, especially in terms of generous spacing between the two tracks).
I bet with tunnels under the suburbs and 300 MPH running, Lafayette LA to Houston TX could be under an hour.