For that to happen, there should be community editions first rite. Community editions will take time to be created. One thing which can be done now is listing the template wikis in the tiddlyhost in a nice UI. On clicking these links, it should redirect to the corresponding tiddlyhost site, where there shall be a download button.
By listing these template wikis in the main page itself, new users can see what all can be done using Tiddlywiki.
This is just an idea which can be considered untill there is a full fledged in-wiki plug in library like CPL. Once that plug in library is active, it should be prominently shown in the home page of the empty wiki so that it’s easily visible to new users
Edit: There should be a way to select the template wikis, because when I checked it now, there are soo many of them. May be use the number of clones as a criterion and select those wiki with clone count more than the cut off limit. Also there shall be some incentive for the creators of these template wikis like giving a creator badge in the talk forum or adding them to the contributors list in the tiddlywiki.com site so that they might keep the template wiki updated.