Hello Jan-Peter
Now heise.de is too on Mastodon for the pleasure of much heise-fans.
I use Mastodon and know many User who wish very well a possitiblity for Sharing.
You Supposing, that Mastodon-User would not insert their Instanz-URL in a Field is not right.
Maybe you only know central kommercial platforms an the convenience of their users.
But in Fediverse/Mastdon we are not so pampered.
All existing Plugins with Mastodon show after klicking a possibility for insert the Instanz-URL.
There is no other Possibiity, I think.
I believe, so much people, who use Mastodon would be very happy, if you would do it so.
The most Users know their Instanz, it is not difficult.
Now I use addanyshare because of Mastodon-Sharing, but it is not so safe like Shariff.
Comfortable vs.Security – than I prefer Security.
Please make a Mastodon-Share with Instanz-URL-Insert an the Web with a Shariff for Mastodon will be more secure than without this.
Thank You for attention.
MfG – Gina