> How can we make Vim9 script, the new Vim scripting language, more widely used?

One way is to inform users and prospective plugin writers that

1) Vim9 script is vastly superior to the old Vimscript, to the point where it is not unpleasant to use, and

2) it is much more conductive to writing text editor code than the general purpose Lua.

Of course this still does not mean that people will want to learn yet another scripting language to write Vim plugins in particular when they already know Lua, but it is very important to be adequately informed about the two above points.