Update 9th August 2019: premium blocks now discoverable for free customers in the block picker, I've changed this issue to be more specific about the presentation of these blocks in the block picker since that's what these designs are concentrating anyway. - @simison
As stated in the documentation:
The feature is available to Premium and Business plan subscribers on WordPress.com and on Premium and Professional plans for Jetpack sites running version 5.2 or higher.
Which makes this block completely hidden for other users.
Here, I suggest:
- Show the block button but disabled
- Attach a tooltip to it (different content depending on Jetpack or WPcom user)
- Link the tooltip to an upgrade screen

And use this pattern for all future blocks requiring a plan.
Update 9th August 2019: premium blocks now discoverable for free customers in the block picker, I've changed this issue to be more specific about the presentation of these blocks in the block picker since that's what these designs are concentrating anyway. - @simison
As stated in the documentation:
Which makes this block completely hidden for other users.
Here, I suggest:
And use this pattern for all future blocks requiring a plan.