I tried it about a year ago because I also really liked the idea. The main reasons why I deleted it again: If you use it with your main mail account you will quickly start to spam people with short 1-sentence messages and if you set up a dedicated deltachat mailbox you will have zero contacts to use the app. So at the end I had to decide between spamming people or stop using it. I still like the idea as such, but it doesn't work for me and my email contacts.
@bjoern why would a dedicated mail account not have access to your contact list? I can see how you would easily be tempted to spam, but yone does not have to use deltachat with every contact, just the ones you would have in Signal/Jabber...
One of the first Mastodon instances, there is no specific topic we're into, just enjoy your time!