See, this is what I mean. We have a bunch of excuses that could be mitigated by that excuse-mitigating juice called "money".
Yes, Trail Creek bridge is a pain. A heavy overhaul and a second track would make a big diff. Given that both parties draw plenty of money from the feds, the feds long ago should've said "wow it is the silliest idea ever to have two parallel passenger lines in frickin Indiana!".
Yes, CSX probably doesn't want South Shore trains as a matter of doctrine. What else don't they want? The Grand Rapids line. It sees perhaps one local and one coal train plus 371/2 every day. Would they give up rights for free? No. But on a half-dead "main" line, trackage rights would go a long way to viability.
There's thirty good reasons we can make ____ solution work, sometimes you have to Just Do It instead of making excuses. At one time there was thirty good reasons not to start the Acela program or buy the Kalamazoo-Detroit line for Amtrak or anything else that's been accomplished.
The new Acela: It's not Aveliable.