Dear Sh.Pradeep Singh Ji,
I have gone through your views expressed above. Still I am of the view that interest earned on account of non-GST business is not required to be included into the aggregate turnover to arrive at the threshold exemption limit. Everything is not always clear in law. It is implied that non-GST business has nothing to do with the jurisdiction of GST. If you obtain registration on the basis of above, you will commence paying GST from Re.One and will be entitled to ITC. You will pay GST on ₹ 4 lakhs (24,00,000 -20,00,000). What I think there must not be revenue loss, after all, rules and regulations or procedures are framed to protect revenue.
When we talk of various definitions such as consideration,exempt supply, aggregate turnover and exempt notifications, all point to the the jurisdiction of GST. Any item which is out of scope for GST network, cannot be dragged into GST network forcibly.
Still if you have any doubt, you may seek advance ruling on this issue.