I would say that sitemaps, though still supported in OH 3.X (and probably in OH4), are rather obsolete and it is probably not worth investing in generating them automatically.
It is probably better to offer to OH3 user a way to use the timelinepicker with the OH3 User Interface. There is already a custom widget that displays a timelinepicker into a webframe-card, as it has been described in this thread. The problem is that this webframe card widget needs to be inserted in an overview page and not all users are familiar with widget programming.
I have written a custom list-widget and a custom standalone-card widget that call the webframe card as a popup. In this way, both widgets can be associated to an item inserted in the semantic model and displayed in the UI with minimal knowledge of widget programming. It is not an elegant solution, as parameters need to be entered for each widget (both list and standalone card), but they can be copy/pasted through the XML code. Moreover, I hardcoded my api-key into the custom widget. The first time the widget is clicked, the creation interface appears while the subsequent ones the saved timeline appears. There is no need in this case to initialize the timelinepicker with the custom file. I have not implemented the administration widget but it should be straightforward (at present I use a very simple sitemap)
I do not know if this is similar to what @mjptec is already doing.
If you think that it can be useful I can share my widgets so that someone more knowledgeable may suggest improvements.