That is a great idea - the weird intersection there really backs up traffic going towards Saw Mill Run which is a main road to the freeway. A roundabout would be great, as long as there was a team of people to keep the green space looking clean and neat.
On the topic of green space, I visited Mckinley Park a few months back and it was totally abandoned and pathetic looking. One asphalt trail runs along the side of a hill, there was a lot of litter and generally nowhere to sit, or do anything. It's a huge park and has so much potential for attracting summertime activity. Maybe more trails, a playground, picnic tables, etc would all help that place out so much.