Color support is important, but 256 has served me well for decades. Can't think of a single program that would benefit from more colors. Unless, of course, you're trying to watch ASCII-videos.
- Themes, its nice to have the same color scheme across your programs. You can always redefine your 16 base colors in the terminal and map these to syntax in your terminal program (e.g. vi), but it's cleaner to have the rgb colors directly in your theme file, especially if you switch themes (I don't do it too often, but I like to change colors every month or so to keep it looking fresh)
- If you code CSS, it would be nice to have preview of #336699 colors in your editor. To implement that, you need real color support.
- And, less important, for those who play nethack-style games it's probably nice.
I'd like to add annotations to regions of the screen about which file / directory a region mentions.
In this way an aware terminal could let you open files by right clicking in the terminal, or change directory etc.
You could even run a program under the shell to check which files were opened and annotate areas if they are mentioned.
(The true-color sequence comes from an ITU recommended extension / future version, T.416². It would be interesting for the OP site to list which terminals support the full proposal, including CMY an CMYK specifications, as well as RGB.)
For example, there are sequences defined to change the title of the terminal window or print to a printer, but they are frequently disabled or left unsupported for security reasons.
True HD color with 64-bit depth, including a 16-bit alpha channel, is the minimum future programmers will demand to syntax highlight our source code and identify monsters in Nethack.
Seems completely unnecessary to me.
(Not to mention we should have drawing support implemented IN the terminal by now).
But seriously, I like the meta-idea of putting up a site to promote a technology; with a list of compliant apps for users, and information how to implement it for the developers. I'm thinking about making a site that catalogues DPI aware software for windows (like Macs "Retina"), because its annoying how many programs don't support high DPI screens properly, and its notoriously hard to do for developers.