Ok, so I just tried the Alternate Personas on the beta server...
It's a little janky, but it actually works.
When you click a different class and then click the create button from the Personas window, it logs you out of your current character and takes you directly to the character creation screen with only the class you had selected as available. You have to choose a valid race for that class. You can set your appearance and your starting stats, and then you login as that persona (aka your alt character).
It will log your new persona in as if it was a brand new character, so in my case, it logged my level 1 bard persona in at Crescent Reach just as if I had created a new character and chose Cresent Reach as my starting point.
Here's the janky part... You start out with everything equiped that your last persona had on (or your main character if you had no persona before. It should be noted that your main character IS a persona). That means that if you were on a level 125 character and you created a new persona, it starts with all your level 125 gear on at level 1... and is all yellowed out because the level 1 character can't use it.
Now for the fun part... When you swap personas, it takes about 30 seconds just as if you was logging out of the game, but then you immidiately switch over to the persona you chose AT the same spot your last persona was at. In other words, if you need to monk flop your way across a bad spot in a zone, you can swap to your monk persona, get to where you want to go, and then swap back over to your Bard or what ever. Other than the time it takes to swap, it's seemless.
I think the inventory sets (save/load) was broken because I never was able to get it to load different inventory sets between personas. The important take away from that though is that you WILL need space in your bags for all of your different persona's inventory sets. Kind of a bummer, but it is what it is.