The new training commands seem a bit off to me from a RP perspective.
Ripping up your fleet structure and reassigning a fleet to a new command seems wrong to issue an order, especially since this means you are effectively training under another CO.
As sloanjh said it is actually "realistic", even though at first glance it seems counter-intuitive. Most modern militaries work this way, in that there are separate Training and Operational commands. Air Forces especially have Basic training facilities from where pilots move to Training squadrons and eventually to Operational squadrons. With the new and flexible Admin commands and OOB handling, it will be super simple to just click'n'drag a Fleet to be under Training Admin for a year or two, and then drag it back to an Operational Admin.
It also means that it's possible to use an otherwise barren system as "training grounds", ie ship is built on Earth, then flies off to a neighbouring system, joins the Training Admin there that's built on some god-forsaken rock, until deemed operationally fit. I can see myself using such methods with a multi-race Sol start to hide Fleet details and for RP purposes. "Captain, you are ordered to report at the Antares Fleet Training Command in six days!"
I was going to wail about that Planet X addition, since I personally think that the science behind it is too iffy but then I noticed it's an optional thing, so I won't
More options is always better though. I guess it could be used for a nifty "Aliens in Sol" scenario, where a sentient race has developed on a moon of a Superjovian out there, and only TN tech allows them to interact with humanity.