Again, that's invalid. "There is no reason room temp superconductors are impossible" is a proposition about reality, that, among all possible knowns and unknowns, there exist no reasons entailing their impossibility. The truth value of this proposition is literally unknown therefore you cannot assert this as if it's true.

My correction was that you should say, "there is no known reason ...", which is instead a proposition about our state of knowledge. This is a correct and accurate claim.

“is” is the present tense of “to be”, which covers our present state of knowledge.

Since you specified no object in your statement (eg. "knowledge") then "is" must be formally translated as an existential quantifier, eg. "there exists". My correction adds the missing object which properly restricts the quantifier.