i don’t have direct answer to this question, but perhaps an alternative (and also perhaps Plugins ideas idea?).
it’s not currently possible (based on my knowledge on obsidian core feature and quite few plugins as well). but this Templater script by AlanG might be useful for you
if u don’t want a too techie approach, i suggest mapping a hotkey to pop up the bracket [[ ]] (i use Ctrl+L). For mobile, install Advanced Mobile Toolbar which will give u bottom toolbar with one of the button to whip out the bracket on single tap.