Ideally yes thats how it is meant to function, but a lot of factors will need to be worked out for this to be implemented. Using credit cards at merchant POS attracts MDR charge which is why many merchants levy an additional charge for paying by CC. Now if RBI and NPCI enable UPI on CC they will have to figure out who will bear the cost of the MDR if they are providing the UPI transaction for free to the customer.
Using this technique it would be very easy for people to keep rotating money between the CC and bank account and using it during the interest free period instead of paying the heavy fees linked to cash withdrawal on CC. To prevent this misuse NPCI will surely levy a 2% charge for CC to CC or CC to Bank account through UPI transfer and maybe CC to merchant transaction may be free if the merchant agrees to bear the MDR involved.