Hi Danny, The stacking modules are not hot swappable. The cables are, but for the modules to be detected they have to present when the switch is booted. A reboot is also required to switch from Ethernet to stacking mode on those ports. Yes the 48Gb stacking modules also have a 3 meter cable.  
I have a set of Dell 6248 switches.  I have a few questions to explore: 1) Can I add/remove CX4 cables while the switch is running?  (I assume this is the same rules as a normal Ethernet cable...) 2) Can I add/remove modules while the switch is running?  First scenario I am looking at: extend stack to an unstacked rack. I'm thinking the process here is, install a spare switch with stacking module, run stack cables back to the stack, breaking and re-assembling the ring, then power the switch up, confirm stack ID and connectivity, and migrate clients over to it.  I can totally hot plug the CS4 cables, right?  Next scenario I'm curious about: upgrade stack from 12G to 48G. Can I swap the 12GB stacking card out and swap the 48G card in while the switch is running or do I need to power off?  At the connectors on the 48G card the same?  (CX4..)  Can I mix/match 48G and 12G cards in a stack during my upgrade process?  Is the cable length limit the same (3M) on a 48G stack?  Thanks! -danny
Dell 6248: hot swapping and upgrade stack links