I didn’t read thru everything, but a dropzone seems to fit your purpose well, especially if the content is already in TW JSON format. If not, you can write your own custom JavaScript deserializer module to further process the dropped string into tiddler/s.
There is a hack, probably not the simple way you are looking for, to create tiddlers using json string by creating your own “$:/Import” tiddler with a specific tiddlers json string format and sending a “tm-perform-import” message to complete the import.
I did something similar also using an input box to capture a json string (nicely formatted by a bookmarklet) and import as tiddlers. I shared it here (Copy info from web site to tiddlywiki using bookmarklet and json tiddler dropzone), look under “JSON TIDDLER INPUT BOX”. The wikicode shared there doesn’t seems like an improvement over yours.
The json string have to be in the “$:/Import Tiddler Temporary Format” ( How do TWs JSON Formats Look Like ) and look like this:
{
"tiddlers": {
"New Tiddler": {
"title": "New Tiddler",
--- other fields stripped for readability ---
},
"Hello World": {
"title": "Hello World",
--- other stripped for readability ---
}
}
}