It will never work, the entire Enhancement tree was designed around Dual Wield, to retrofit 2h back into it would require a massive balancing effort, with many, many abilities that would need to be changed.
Also, its not as easy as it sounds. Lets use Stormstrike and WF weapons as and example. If you balance Stormstrike around the idea you use a 2h weapon, then you would need to make sure its damage isn't too high for a instant 2h strike otherwise its damage will be to high in PVP. You'd also have to re-balance windfury weapon. You wouldn't be able to have WF weapon procing an extra two attacks+ additional AP on top of having a huge 2h strike because the burst would be ridiculous.
However once you balance those abilities around 2h weapons you find that they suck for DW since they don't do enough damage, you can't buff DW damage directly because that would mean 2h damage goes trough the roof. I'm not saying it isn't possible, but its definitely no worth the effort to do. Blizzard realized this very same thing and that why they decided to take shamans in the direction of DW and scrap 2h, because it was mathematically unviable to balance both within the same tree, and it still is.
So, if you want to bring back 2h viability, don't simply say you want 2h viability, start working on some theory crafting on how to make it work, invent new abilities, run simulations to see how both scale with different stats and on different levels, compare DPS numbers and submit them to Blizzard. Otherwise 2h DPS is dead and will remain dead for shamans, forever.