They have a very strong policy against duplicates, to the extent that questions get closed as duplicates even when the original question has no answer.
Asking two duplicate questions (even if upvoted) already leads to a warning about a possible question ban.
The same may happen if your feature-request gets (massively) downvoted - post quality and acceptance of opinion are not clearly separated.
Meta Stack Exchange is not a child meta site. It's a full-fledged stack exchange, just like the Ask Ubuntu main site. As such, yes, it has its own reputation system, along with all the same mechanisms for post bans that you'll find on the main site.
Just like any other Stack Exchange network site, all the same rules about doing prior research, not posting duplicate questions, etc., all still apply. Heck, those things are supposed to apply to child metas as well, so I don't understand where your apparent surprise is coming from.
Also, Meta Stack Exchange actually has less strict parameters for getting post-banned than on other Stack Exchange sites (it's supposed to be about 6x less strict, it's in an MSE post somewhere). You'd have to work pretty hard at being awful in order to earn a post ban on MSE. Here's a tip: before you start making unpopular feature requests, go answer a few support questions, so that if your request does get downvoted, then you won't be so close to a question-ban.
Finally, just like on a child meta, Meta Stack Exchange's voting combines post quality and agreement/disagreement into a single upvote/downvote.
See also Get rid of the question ban on Meta; suspend actively harmful users manually.