In theory, I would love a 24man premade only mode, the games would be exciting, there would be a challenge. But in practice? The queues will die much faster. 8v8v8 isn't suited for premade only, 2 teams may tunnel and let the third team win by objectives only (which I have seen plenty of times), 2 teams may queue with the intention to join forces and base camp the third, win trading would be able to happen much easier.

Premade only mode also still won't address the Maelstrom solo queue problem, without premades in the mix, Mael still gets their easy wins vs the players who AFK, bot, give up because they didn't get placed on Mael, etc. Why should the players that decide to solo queue who want to put an effort into improving and winning funnel into one GC and spend hours queuing just to get competent teammates? Statistically from the frontline standings for the past few years, Maelstrom always has the higher win rate, because it is essentially the premade without forming a premade.

What we need is an 8v8 mode, like capture the flag that is premade only. It would pop frequently only requiring 16 people, it would be fair having no third party to influence the outcome of the match.