Yeah it seems extremely challenging to figure out.
I have 1 idea, which keeps with the same platform you are using now.
What if once a month, something from the top 20 or 30 suggestions could be implemented, and in the update page, it could be specified that the feature was added "as suggested by the community".
After adding, maybe the suggestions can be reset monthly, which would make sure votes are always recent, and not some abandoned vote from a few users 4 months ago.
This could give Scirra the choice to cherry pick something that Scirra agrees with, but also Scirra can pick something that is doable alongside other features that you guys are currently working on.
This might get people more engaged with the sub platform, as they'd get excited when they see on the update page that a community suggestion was able to get into C3, and the sub platform would be blank after this, fresh and ready for everyone to post ideas (or repost their old idea since they're so eager for it).
I'm not sure. I really like the idea of being able to influence C3 though, as many others likely do. I wonder what could be tried.