I don't think GitHub has any feature that allows for limiting submissions per user, so we couldn't enforce that easily - but I don't think we should do that anyway. The process is basically a collaboration between users saying what they want and us reviewing what we think is important and feasible. When things are positive on both sides of the equation it is much more likely to get done (subject to available resources). Limiting submissions means it's less likely to get a positive result on both sides of that equation, and also tends to make people upset as they have ideas that they want to submit but can't. The downside though is the huge volume. If people go ahead and submit roughly 2 years worth of work in the space of 3 days - which is what I think has just happened - I don't think there's much we can do about that, other than encouraging people to only file a small number of their most important requests. But I don't think anyone pays much attention to that!
I also don't think it's feasible for us to respond to every suggestion. The feature request guidelines say we don't promise a response because I don't think we reasonably can. Even minor features can become unexpectedly complicated, and so I don't want to give a "this looks easy!" response even if I think that, because regularly it descends in to weeks of complicated work anyway, and in the worst case could end up having to be removed again, and so such responses would be misleading. Often responses end up in extended discussions where people dissect what I've written (which was usually only a vague impression anyway), try to advocate their case more strongly, or end up talking in detail about various aspects of the suggestion; I just can't afford the time to do that for hundreds of feature requests, nor does the discussion even always come to any particular conclusion. The only feedback I'm comfortable giving is "this looks particularly difficult and would likely be a major project", which unfortunately has the side-effect of making me look really pessimistic and only ever saying negative things about suggestions. I don't really want to give that impression as it's a useful and positive thing to have lots of cool ideas being submitted and discussed by members of the community who care about making Construct better. But I'm not sure there's anything better to do - when there are such a huge number of suggestions, way way beyond what we could possibly do, I think it's sensible to manage expectations and push back where I can to help identify what really matters.