With the introduction of the Catalyzer line, we got a gun with essentially a charge/normal combo attack. Fire out some charge orbs, hit with a regular shot and BOOM! Hours of fun (if only I had one...).
It occurs to me that adding a charge/normal combo to the sword side of things might also be rewarding. I find that for the most part there's some swords I only use regular attacks with (Cutter line, I'm looking in your direction), and some swords that I mostly use a kite-and-charge technique with (hello Brandish line). It'd be neat to have a sword that encourages mixing things up.
For example, have the sword accumulate a charge by landing normal hits, to power up an otherwise weak charge attack.
Alternately, have a sword where successfully landing a charge attack gives you a buff on normal attacks that tapers off for 5 or so seconds.
there are some issues with the catalyzer, namely the time it takes to attach charged orbs and detonating them before your allies mow them all down.