Just wandering around my brain-clutter bin and this left out. Generally I don't get crazed about Rex becoming force sensitive. He's badass enough just rocking his guns.... buttt I can't deny this is sexy as he'll.
P.S. (especially for the Rexsoka shippers)
Forgive me if my reasoning isn't entirely cannon.. but I'm relying on info that I probably read once on Wikipedia or something... Since lightsabers don't necessarily need a kyber crystal as a core, other totems have been used in the past, as long as the user can properly commune with them and forge them in to a conduit for the force to flow through. So I thought maybe he didn't have a way to obtain a crystal and instead chose to use something he cherished - the head-dress Ahsoka wore as a padwan. It is made from the teeth of a beast that her people face off against as a right of passage. He uses pairs of these in each blade; their song is deep and rich like whale-song. The pointed end can lock the two together, a la light-saber bo staff.
OH! OH! And cuz its cool and he's all mandelorian sub species and... he ignites the blades.... and they are dark saber esque....
(continues rambling mindlessly)