They just haven't worked well since alpha. Their pathing and AI sucks. You obviously aren't going to give us a pet bar for them and let us control them. They're weak to AOE damage, minimally useful in coordinated pvp, useless while tanking, and mildly useful (but ultimately low on priority) for raiding. You're better off skipping them to min/max for raiding.
From what I've noticed, the only thing that they are REALLY good for is soloing elite quests. That's really it, and it's a pretty poor end game use.
So just scrap 'em.
Give us a new talent that would be more universally useful in more situations, and not just for leveling.
What about something like an improved death strike?
3/3 points: Every time you score a critical strike, you have a 33% chance to gain imp. death strike buff (whatever you want to call it). This makes your next two death strikes cost no runes.
There you go. Similar healing, useful without poor pathing and AI, controllable, no blood worms running around getting themselves killed and pulling adds.
Get crazy creative with the proc method, but it might be time to just scrap the little worm guys and turn a new useful ability (the new deathstrike) into something more useful via a mid blood talent. This would also share wonderful synergy with death rune mastery, and set up for some nice burst.
They're just currently pretty "meh" once you get capped out in levels, and start assuming end game roles.
Blood worms are like the new vendetta (and they've made vendetta basically obsolete), but a lot better, and don't require a KB. That's great, but I just don't see these guys being all that useful later on. It certainly does add a lot of flavor to the class, don't get me wrong. I love the blood worms when I'm farming, leveling, or taking on elite mobs. Heck, they're even OP in 1v1.
I just think that you could get a lot better use out of free death strikes (which would become free blood runes via DRM, which do fantastic damage via heart strike, which would become free crit death coils via sudden doom, which would become free bloody vengeance procs). That kind of synergy is really hard to overlook, and would provide far more use for end game scenarios in just about any situation.
Again, just my opinion.