If DNA price will push IDENA to top 100 CMC we will most likely see 100 000 nodes, because 1 person from third world country will bring here whole village (of course this one with internet connection).
According to your calculations, to get Idena in top 100, we will need a price of $1, and with the
Fakmi Ifajno statement that with 100K nodes we will get 15 DNA/Month I think the numbers of nodes will get lower since many users will loose interest for $5-10 a month return (what you get minus expenses i.e. VPS rent, electricity bill).
I don't think we will see more than 10-20K nodes, since the return will start to get very low after at 1$ price.
At curent price with 1100 nodes, you get $125 per month (flips rewards, invites excluded). With 5K you'll get around $30/Month which is still profitable. More than 5K will make running a node unattractive for many.