She can do nothing against siege, lower her W CD will be the only effective way to make her mid again.
She does not have enough mana as a support to constantly W anyway, Riot just does not want morg to be mid.
Morg clears waves entirely with level 3 W. Safe and effective wave push was one of the biggest reasons she was played mid back in seasons 1 and 2, and that was back in the days when turtling strategies like the CLG EU "no kills for 30 minutes" waveclear-reliant stuff was going on. I don't think this is her problem.
She might not have the strongest push but when built full AP she can clear a siege wave pretty fast while not having to be near it. She has a 3 second root, shield that stops CC, and an AOE ult that slows then stuns. Her W does not need to be buffed. If you don't think she's viable mid then play her as a support. Not every champion needs to be able to mid efficiently in the current meta. The only reason Riot needs change a champion is if that champion was extremely weak or broken. Morg is neither, but she is strong.
And in other news, 
Lee Sin can't jungle, 
everyone plays Aatrox, and 
Syndra has horrible burst.
She can do nothing against siege
She can throw long range Q's when she see's an opening between minions. She can use her shield if she see's the enemy team try to engage, she also has her ult to deter engages on her team.
Full AP Morg is a more than capable mid-laner and is actually pretty safe. W is good at wave clear and Q/R can be used offensively or defensively. E is a great defensive spell. Landing a q+W combo with full AP build chunks people
Wut? She does have wave clear and her Q is one of the longest skill shots in the game. She can do fine against siege with her Q and her own E, and then of course just wave clearly with W. if you build her full AP then one W clears the waves. Oh, if you go mid you'll prolly build full ap.
She was a mid laner before this season when people wanted her to be a support. Literally nothing changed besides her numbers and that was after people started taking her support. Same with Annie and Zyra. Those are mid lane champs that people took bot lane to crush lanes so they'd have high early game damage with good early/mid game ADCs.
Play her in a custom or bot game and watch how she has consistent wave clear throughout the game when built ap.
If you want her w's wave clear buffed, then its damage to champions stuck in her root will have to go down... As somebody who loves mid Morgana, I wouldn't mind Riot hitting the duration of her q in exchange for raw damage on her w - Total damage from q-w would be about the same, but waveclear would be stronger and w would be more useful if you miss the q. That said, if you're having trouble with an Ori seiging too hard, just freeze lane in front of your turret and wait for your jungler to gank
I'm pretty sure at some point in season 4 preseason they buffed the amount of gold supports get from having a lot of assists too. They may have even boosted idle gold generation and I think the gold generation masteries are a bit stronger too. Not sure how much of an impact all this has, but I'm sure it's giving supports a little bit of extra spending money compared to S3
