We run a TL-1 and the distance between centers has never been an issue. In fact, you could have 18" between centers without a problem if your not working with a steady rest. We don't run it manually very often, as it has performed beautifully in full CNC mode for fitting barrels and I've made numerous other parts and fixtures on it.
I have not tried fitting a barrel with the CNC before. It's something i've always done on the manual lathe. I'd be curious what you would use to hold the reamer.
Generating the thread and even roughing out a partial chamber would be rather easy i guess if your head stock was short enough to be access the opposite end
of the barrel for indicating. Mine is way too long so I've never even tried.
I am running a TL-1 as well. They are pretty capable machines but obviously require more investment than a manual machine.
One limitation I haven't seen mentioned yet is the width of the headstock which pretty much doesn't allow doing barrels between spider chucks on each end of the head stock. I started out this way and made my own spider chucks. My chucks only added about an inch more of length between the ends of the spindles and that made them about 24" to the center of the clamping bolts. Working with shorter barrels required threading an extension on each end. I threaded the muzzle with sacrificial threads to allow the extension, and then cut them off when cutting the bad inch off the barrel anyway. I didn't feel this was the best approach for efficiency or results, and luckily Nate made his TBAS available about the time I was looking for a better solution. Check that out from Straight Shot Gunsmithing, who is also running a TL1. I've been using it with great results.
As for holding the reamer, you are going to want to attach it to the tool post so you can use the carriage. Don't rely on the tail stock on these machines for anything that requires it to be concentric to the headstock, they just aren't. I'm simply just using a gre-tan reamer holder and a morse taper tool holder on the tool post. I'm aligning it in both x and y axis, by indicating in a collet chuck to perfect alignment, then putting an indicator in the collet chuck to align the tool holder. I'm pretty confident in my alignment to .0001 to .0002 with tool changes going on, which is about 100 times better than you are going to get with the tail stock on these. You can run the carriage with the hand wheel and have a DRO and control to .0001 on the Z axis. That makes head-spacing pretty easy!
I think the best feature on these though is the "thread-repair" function built into the Intuitive programing mode. With a bit of thinking outside the box on the setup, this can be used to easily pick up the thread in a receiver for receiver blueprinting. Once a receiver is dialed in, my blueprinting cycle just takes a few minutes and that is making really light cuts and running the rapids in grandpa mode.