Adding 2D graphics entries to termcap/terminfo?

I have a bunch of terminals that have 2D graphics support.  For a
while now I've been thinking of adding custom term{cap,info}
capabilities to describe the ESC sequences needed to draw graphics
primitives: point, line, etc.

I ask you ncurses gurus: how feasible is this?  Obviously only my own
programs would be using these capabilities.  Is there a convention for
defining private capabilities?

For reference, I don't think anyone approached things this way when
these terminals were being used (late 70s through late 80s).  Instead,
I think they used something like GKS which had the smarts to turn API
calls into ESC sequences for the various terminals that were
supported.  However, if terminfo capabilities were added then the GKS
driver could avoid hard-coding the ESC sequences and use the
capabilities to target a wider range of terminals.
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