Good luck with that.
Widgetkit, like ZOO, is using JSON storage, which is a little bit tricky for Seblod to manage.
By default, Seblod stores JSON value in a second level attribute, using the first level for just field name attribute, which would be the first thing to overcome, since Widgetkit has a lot of first level attributes (name, id, type etc.). Second level attributes are images in "captions","links" and "settings" attribute, which can be accessed easily (storage JSON, field name[attribute]). Also, you might have to escape the image paths (it occurred to me that escaping might be managed by Seblod JSON store). Another thing is that you have to do it in BeforeStore event, since technically you are storing it in #__widgetkit_widget table, and you have to obtain new widget ID, so that you can use the plugin content during store of the content. Unless, of course, if you plan to have 2 distinct steps - creation of widget and creation of content that will contain the widget.
An alternative, if you want to stick with Widgetkit is to use plugin in content - [widgetkit id=25], that could be feasible if someone manages image upload + gallery creations.
Another way to create gallery would be to use "vanilla" images in FieldX and use typography Image on the field.
{"type":"gallery",
"id":25,
"name":"Demo Wall Polaroid",
"settings":{
"style":"wall",
"width":200,
"height":150,
"order":"default",
"effect":"polaroid",
"margin":"",
"corners":"",
"lightbox":1,
"lightbox_caption":1,
"spotlight_effect":""},
"style":"wall",
"paths":["\/yootheme\/widgetkit\/gallery\/polaroid"],
"captions":{
"\/yootheme\/widgetkit\/gallery\/polaroid\/image1.jpg":"Tony",
"\/yootheme\/widgetkit\/gallery\/polaroid\/image2.jpg":"Susan",
"\/yootheme\/widgetkit\/gallery\/polaroid\/image3.jpg":"Jennifer",
"\/yootheme\/widgetkit\/gallery\/polaroid\/image4.jpg":"Kim",
"\/yootheme\/widgetkit\/gallery\/polaroid\/image5.jpg":"Vanessa",
"\/yootheme\/widgetkit\/gallery\/polaroid\/image6.jpg":"Clark"},
"links":{
"\/yootheme\/widgetkit\/gallery\/polaroid\/image1.jpg":"",
"\/yootheme\/widgetkit\/gallery\/polaroid\/image2.jpg":"",
"\/yootheme\/widgetkit\/gallery\/polaroid\/image3.jpg":"",
"\/yootheme\/widgetkit\/gallery\/polaroid\/image4.jpg":"",
"\/yootheme\/widgetkit\/gallery\/polaroid\/image5.jpg":"",
"\/yootheme\/widgetkit\/gallery\/polaroid\/image6.jpg":""}}