Why not, indeed! So here are some answers to your questions, from Mojang CEO Carl Manneh!

Realms Q&A:
Will this service limit you to only allowing people to reach your server if they are in your area?
- Anyone who the server 'owner' white lists can join your server, from anywhere in the world. Obviously you'll get better performance if you are geographically closer to the actual server.
Will it allow you to add plugins?
- Starting out it will be vanilla Minecraft only, but as our API matures and Realms is further developed, some sort of plugin connection may be possible.
Will players have something like FTP access, to upload worlds, mods, and manage server settings?
- Yes there will be a settings panel for the server owner. It will be quite limited from the beginning, but will be built out as the service develops.
Is this service aiming to replace third-party hosting?
- No. We will not be able to provide all the options and features third-party hosting provides, so there will definitely be a need for third party hosting.

There you have it, even more goodies on the upcoming Realms service! A big "thank you" to Carl for giving us some insight into Realms, and answering users' questions directly!
Probably get some TL;DR's in here XD
It shouldn't impact small community servers much. The most likely outcome, if Minecraft Relams is done well, is that smaller communities will move from hosting an expensive, unreliable server, to purchasing an affordable Minecraft Realm. My server is relatively small, with about 8 relatively active players and so far, Minecraft Realms seems like it would be a good investment for me.
By the way, does anyone have an accurate estimate as to when this service will become available?
The way it seems to me, MC Realms is good if you have a few friends (1-4 or so) and want to all adventure on MC together, but can't for some reason have a LAN party together. (bad internet, don't live close, ect)
Then the normal servers are a good place to meet new friends that you may then invite over to the MC Realms to play with or If they prefer to have the challenge of having to deal with griefers. Another point is that some servers have is Role Playing, there are good jail servers and adventure themed servers that you can't recreate with just 1-4 people using MC Realms
I think the 2 may be similar in some senses, but WILL still be different enough to coexist together
I didn't say all were o.o. I host servers too, but for fun and inspiration, not money. I do know many server hosts out there though are only doing it so they xan hops to get loads of money..
I believe Mojang stated it would be released towards the end of this year
Will this service limit you to only allowing people to reach your server if they are in your area?
- Anyone who the server 'owner' white lists can join your server, from anywhere in the world. Obviously you'll get better performance if you are geographically closer to the actual server.
Will it allow you to add plugins?
- Starting out it will be vanilla Minecraft only, but as our API matures and Realms is further developed, some sort of plugin connection may be possible.
Will players have something like FTP access, to upload worlds, mods, and manage server settings?
- Yes there will be a settings panel for the server owner. It will be quite limited from the beginning, but will be built out as the service develops.
Is this service aiming to replace third-party hosting?
- No. We will not be able to provide all the options and features third-party hosting provides, so there will definitely be a need for third party hosting.