More a case of "if". If the vendor wants to write a Connect version of the add-on, then you'll be able to use that (Connect and type-2 add-ons are very different things)
Hopefully they'll tell us here that they're working on it!
I created an issue for you here: https://bitbucket.org/madein49/slack-for-confluence/issues/1/request-make-a-cloud-version-of-this-add
This type of question is better to ask the add-on vendor directly.
Hi my Community friends! For those who don't know me, I'm a product marketer on the Confluence Cloud team - nice to meet you! For those of you who do, you know that I've been all up in your Co...
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