The billionaire businessman tells TMZ that Emma Grede -- the co-founder of the Kardashians' fashion empires SKIMS and Good American - would be "insanely good" as a full-time Shark ... having guest-starred on the show before.

Mark heralds the 41-year-old as a brilliant entrepreneur ... with an extraordinary knack for helping companies grow with her experience.

What's more ... he's impressed with her natural ability to connect with others ... and says her television charisma also makes waves -- though, as of yet, auditions to find his replacement haven't begun.

Mark also gives us a splash of context on departing 'ST' -- which he first announced on the Showtime podcast "All The Smoke" Monday ... telling us his decision is rooted in wanting to hang out with his brood as he usually films every summer during family vacation.

He says at 14, 17, and 20, it's not long before they leave the nest ... so it's understandable he's cutting back.

As we previously reported ... Mark's also selling his majority stake in the NBA's Dallas Mavericks after buying the team in 2000 and overseeing the franchise's most successful run and only NBA title ... so the 'Tank' isn't the only thing Cuban's leaving behind.

Despite "Shark Tank" nibbling away at his personal time, he's cherished every aspect of the show ... from what it represents to the impact it's had on the next generation of entrepreneurs.