Yes, there are still impossible researches in TC4.
People should just trashcan the ones that look possibly impossible and get a new one. All it costs is a piece of paper and one point of the original aspect.
What you don't want to do is waste a bunch of aspects and time on one that is impossible. Make your decision at the beginning, not the end.
What I do when I get a new one is this.
1. Can I draw a relatively smooth path between all the points? If there is a node out in the middle of nowhere that requires you to go out to it and then almost the same path back just throw it away.
2. Is it one of the 2-3 node researches from the addon(s)? If so are both the links more than 1 jump wide? Throw it away.
3. When drawing that circle look at the first jump in either direction from the start node. Go in the direction of the shortest one. Since you don't have to connect the side you don't choose, don't choose the longest side.
Do those three simple things and save yourself some frustration.