I have trouble imagining how a shardspear should work - wouldn't it get stuck all the time?
Shardblades are efficient because they cut trough anything - the tip of a spear could work similarly, but the shaft would get stuck all the time (blades can get stuck if twisted the wrong way if I recall correctly from the novel). Also, shard weapons are basically weapons of mass destruction because of their slicing power. Stabbing may work, but it's vastly less efficient when facing many opponents. Slicing large groups with a spear is not good, because if one guy gets a little closer, you hit him with the shaft, that doesn't slice and the spear is blocked.
Of course, you could say it's a spear with a short grip and a very long tip, but then really, it's a sword
I think it will be much more interesting to see the impact of half-shards on shard combat - current shardplates are basically 2-handed swords in their use pattern, and that combat style is very disadvantaged when facing a sword-and-shield opponent. There are actually many strategies that could mess up the current type of shard combat, and I predict that we will see quite a few new approaches not just based on surgebinding powers but also on intellectual progress.