Storing images and video on-chain is expensive. To support media in a decentralized way it must be stored elsewhere. IPFS would be added to the current options (Imgur, Youtube, etc).
Yes, that was the original plan. If you look at the source of the protocol page there's an action commented out for setting a base URL, basically a content hosting provider.
what's the difference between running a central server and running an IPFS node? You need a server anyhow. With IPFS people can help hosting their own files.
One benefit is that it doesn't require DNS or even a public server. You can run a local Memo client that uses IPFS. Another nice thing is it has built in easily parsable hashes.
Uploading directly integrates the media effort and the posting effort => will prompt more participation (less hesitation about going offsite to get URLs.