Hi there,
the Block replacement for widgets is still an experimental feature of WP. So implementing this will be dependent on when WP release it. It will also depend on existing plugin developers to convert there widgets to blocks – or rely on the Legacy Widget Block ( which is also under experimental )
But in the meantime you can already use the Block element to add any block generated content to any hook within the theme or replace entire theme elements such as the sidebar.
And if you require a traditional widget area within that content you can use this plugin:
https://wordpress.org/plugins/organic-widget-area-block/
Block Elements also benefit from Display Rules, so there you can dynamically display these … something that isn’t yet covered in WP’s plans.