The FAQ seems to imply that Minecraft on mobile devices can still access servers directly via IP address:
But nothing about Minecraft on Windows 10. For now you might be stuck with the three approved (so far) servers, Mineplex, InPvP, and Lifeboat. I'd expect many more servers to come on line over the next several months. Lots of money to be made for good servers.
Actually Minecraft Windows 10 does still have the option to manually type in an IP address. If you go to Play>Servers> Add Server You can add another server.