I have an 11' inflatable with a 20HP -and it goes 25 mph. I can't see that boat that weighs twice as much going 20 mph with a 6hp, if they ever get to making one.
They don't even make 6hp props with enough pitch to go 20.
there's a company in Norway (pioner) that has been around since the 50's - they make rotomolded boat 11' -rated for 15hp
they will pull a tube or skier
^really exists
that "marinekart" looks like some kid doodled it up in CAD
we had a 12' Porta Bote with a 6 hp Johnson .... with one person it would get up pretty quick an go on down the lake .... with two it would get up and get you there eventually .... with three it would plow along slowly with the motor wide open