There are numerous ways now how the shard problem could be addressed without removing or even changing the mechanic of collecting souls significantly. The detailed methods are as follows:
   Above all you can remove soul cost for damage abilities. This would allow us to actually consider using shadow burn and soulfire without having to think about our 'fuel efficiency' all the time.
Sometimes you are able to allow souls to be redeemed from low levem mobs which in turn would make low-level instance runs a lot less tedious and allow soul shards to stack. Stacks of 5 would be plenty, we'd even settle for stacks of 2 which would stretch my shard carrying capacity and reduce inventory waste.
It is a must for you to give us an ability that takes the souls from nearby bodies. So if you're standing in an instance and there's trash mob corpses all over you hit your new 'redeem' ability and all the corpses turn into nice little soulshards (if you have looting rights).
Add soulshards to the currency tab removing the need to inventory manage the darned things.
Make bags automatically replenish shards as you kill or over time (a free shard every 15 minutes would be a godsent in itself).
There are lots of simple things that could be implemented to alleviate the Warlock's infinite problems with soulshards and there's no reason why collecting soulshards should be so much of a chore.
You just wasted 30 minutes of your playtime on something that gives you nothing other than the ability to cast spell if it takes you 30 minutes to farm the required shards before you can play your Warlock.
If you had to go out and store up non-stacking snowballs to cast Blizzard, are you willing to play a frost-mage? If you had to get in collect individual bits of magma to cast pyroblast, are you willing to use it? If you had to have a spare shield in your inventory for every time you threw your avenger's shield, how would you feel about protection Paladin? If you couldn't buy bullets/arrows from a vendor but had to manually craft them each and every day, how much would you enjoy your Hunter?
   There are all very off-the-wall examples but a Warlock without soulshards can't function at its optimum and having a limit to how many shards you carry means that there's literally an 'invisible' cap on how long a warlock can last in any situation.
Let us look at this from a cost perspective:
If it takes you 30 minutes to collect about 50 shards and it takes you about an hour to farm 100g that means that every soulshard is worth about 1g.
That adds up quickly in a normal day's worth of play. In part, it adds up even quicker in a raid and it's just plain ridiculous when you start using your shards to taxi people all over the place.
To be honest, we really do not mind spending a shard on summoning a demon, it make sense that they would need a soul to consume since they are demons after all. Are there soulfire and shadowburn? Those spells have been normalized ages ago. The damage is far from spectacular and doesn't warrant the soulshard requirement.
Do we even remember what the soulfire animation looks like? We discovered spell with the new backdraft haste procs but now we are going to have to bench it again simply because we do not want to drag 70 shards around just so we can cast some hasted soulfires.
Something needs to be done and something does not look so difficult. But why is nothing done about the soulshard situation?