Please, no. The problem with challenging content with a high number of people is not the content itself - it's the logistical nightmare of getting 24 competent players, who are more often than not adults with reponsibilities, online at the same time, on a regular basis. 8 people is manageable. 24 is not. You would end up spending a lot more time on PF queue, or in case of a static, having to call off raid nights because someone couldn't show up. Or keep players benched, which is not fun at all.

FFXIV needing only 8 people to do the hardest tier of content is a blessing. Don't squander it.