It's a nice idea and certainly very useful, even for streaming our content ourselves when we're on vacation or outside the house. You can already do that with 3rd party software, not integrated into MC.
However, there are some additional considerations that make it a bit dangerous to share content:
- upload speed limit: most internet connections are asymmetric; the upload speed is much lower than the download. By streaming media, your upload can get saturated even with a single video stream, depending on quality. When that happens your DL also goes down the drain due to delayed ACKs.
- realtime transcoding sucks. Poor quality, and high CPU usage leading to fan noise and heat. Can't be done on a cheap HTPC, requires a good CPU or an expensive GPU. This can be avoided by doing direct streaming (no transcoding), but that only works for some video formats like MP4 (MKV won't work, for instance), and uses up more of that upload bandwidth.
- Sharing control: by giving a link to someone, how do you make sure that it won't get re-shared over and over again until you lose all control? Parents share the link to the daughter, who shares to a friend, who posts it on facebook; BAM, you now have 50 people accessing it, and there goes your internet connection until you block it.
- Related to the previous one, there are legal implications of sharing content. It's fine to share your home videos, but if you share a movie you legally bought and ripped, and then lose control and it gets widely shared or even torrented... tough luck, you're now liable.
I have remote access to my collection for when I'm on vacation, but I only use it for myself. When I need to share something to family/friends, I still do it the hard way, usually setting up a time-limited FTP/HTTP download, or uploading a home video to my (private) youtube channel.
One easy way to share content from your home is to set up an HTTP server. You can then have links to individual files, optional user/pass authentication, and direct streaming even works for MP4 and some other formats. Just... not integrated into MC.