For the rtePlugins used in a dialog, it's necessary to define them in the inline and dialogFullScreen nodes in the toolbar property.
You also need to make (for paraformat, styles) a popover definition with an "items" field: for paraformat this is "paraformat:getFormats:paraformat-pulldown" and for styles it is "styles:getStyles:style-pulldown" - what should it be for the insertvariable plugin? is it "insertvariable:getVariables:insertvariable-pulldown" ? Because I tried that and it's not working.
The inservariables plugin was provided by personalization/MCM, this never got ported to Touch UI (as the team has moved to Adobe Campaign from AEM/CQ MCM implementation).
There is a Touch UI-compatible version of the Adobe Campaign insertvariable plugin (which gets the variables from a AC instance), so you could use this as a starting point for creating a custom Touch UI-based version of the original insertvariables plugin.
Your entry point would be /libs/mcm/campaign/components/touch-ui/clientlibs/rte/personalizationplugin/plugin.js