Let me elaborate a little about what I said before.
The idea to have speedpaints in the movies portal was pretty scary at first, because then it would most likely flood the portal, but... having speedlapse/timepaints be available through the art portal isn't so bad. The thing is, those speedpaints should only be accessible through individual submissions (like I mentioned in my last post). I mean, watching a timelapse without first seeing the art piece itself is pretty pointless. That would prevent any portal from being flooded, since you could only view the speedpaint though its respective submission. Having it be a seperate category in the art portal would be kind of redundant, though.
Problem is, we can't really utilize anything on newgrounds for this at the moment. Some people mentioned the Dumping Grounds, but how the heck are you supposed to watch a 5-7 minute video through that. Maybe we could have some sort of option to submit a movie through the project system as an unlisted submission (like youtube's private videos). Then have a place to put a link to that speedpaint in the art submission and there ya go - no more redirecting people to youtube for speedpaints!
So having this some-sort of a sub-portal for the art portal, tailored for speedpaints, would be alright. Then everyone, those who want them and those who don't, would be happy.