I'm also planning to do the same considering my LTF Regalia is useless except for Smartbuy usage and Tata Neu is okay as I have FYF and HDFC denied making it LTF I will comfortably hit the milestone for making it free so might retain it. For some reason, HDFC had my defunct Moneyback card still active in netbanking and CIBIL additionally it is also linked to my Regalia which I suspect is causing HDFC to not give me uogrades or LE. I have a couple of EMIs on Regalia and intend to close it by next March or so. And, freshly apply for a better card ir maybe not at all considering Tata Neu is a better card to have than Regalia Gold atm. I'd use my Airtel Axis, AMEX cards for my usage and see what HDFC offers me as pre approved offer to proceed.
I just hope having a co-branded card active won't impact me in getting a new card from HDFC considering how shitty they are.