That video answers a lot of questions, the most interesting parts are towards the end:
https://fb.me/e/1ZbJXm3Sq
So, yes, the boat is a Sunfish hull, all "known issues" have been addressed (e.g., backing plates), all parts are backwards compatible.
When you click through the "build your boat" pages at the SERO website and choose the cheapest options for blades, sails,... no extras, the price turns out to be
$5200
That is exactly the price of the Rocket.
Someone did their market research.
Looking at their website:
https://seroinnovation.com/index.php?route=common/home
My impression is that the SOL is basically the Sunfish hull with a new deck/cockpit. All the other parts (mast, sail, bailer,...) look to me like Sunfish parts.