Interesting to read all the comments. Thanks Dave S. for the posts. So far it seems like there's three individuals who might be interested in this. I'll work with them off line and see if they want organize.
Regarding $$ and pollutants... We've got the money from a voter approved levy and can't redirect it to other "worthwhile" projects with 3/4 of City Council voting to do it. Seattle isn't closing parks, though were are reducing maintenance since that is paid for out of the City's general funds. Those have taken a big hit.
The Puget Sound Air Quality folks and King County Health. They agree that it's best to exercise out of cities and on mountains (ding, ding you guys win!) Neither organization has any data about what levels of pollutants we might find under I-5. We may work with the County to get some monitoring. Recreating at this site should not be too much different from elsewhere in the City. People regularly run the stairs nearby, bike to work along congested streets and run everywhere.
So, we all balance exercising locally and not driving/polluting to get to fresh air with increased air pollution.
Ironically, the only beasts on tethers would be...some of you guys.
David