Tender plant = root of Jesse
Without form = God
Comeliness no body we desire= crucified Christ
You can say they mean whatever you want, although I don't think you made a very good attempt there. The point is, people avoid it because it's not as easy to manipulate away from its original reference: that the Jews were God's Chosen People, whom he nurtured like a tender plant, but whose kingdom fell apart and was without form, and not terribly appealing. It doesn't require manipulation if you just read Isaiah in whole and accept that it's about what it says it's about. But I forget, modern-day Christians believe they understand Jewish writings much better than Jews do.