Couldn't you just do something similar to Minecraft where the launcher has the option to use an older client version for servers / mod packs that only support that client version?

That way you could move forward while retaining playable support for older titles. I mean, I do have to say that if developers have abandoned a project and are not seeking to change it any further, then I don't see the point of holding things back for them.
Minecraft is a really bad example to draw from.

They've been promising us plugin developers an official modding API for over three years now, and have utterly failed to deliver. I stopped working on bukkit mods when dinnerbone said that bukkit was going to be a thing of the past in "just weeks" at minecon 2012.

Here I am, with four dead plugins that don't work because version compatability breaks every single release.
Being honest, I don't see how it is smart to be removing any features/functionality, as long as they don't become an issue.
Improving upon these is probably better than to remove them. And I think BYOND could gain a good deal of things from improving upon what it has.
In response to Laser50
The problem isn't removing features, it's adapting the language to work in different ways so that new features can be added, but in adapting those old methods it breaks precisely how some of the functionality works. Not makes the end result different, but the means different.

Page: 1 2