Will you have a happy client when the term premium gets delayed in the mail and the policy lapses along with the forfeiture of the return of premium benefit? What happens if the client has short-term financial problems and can't pay the premium?
Run the ROP term premium against a current assumption UL with the same face amount (and premium). You'll find equal if not better performance of the UL product (on current assumptions), plus a "safety valve" of either being able to surrender the policy before the end of the ROP funding period or to skip a payment or two. Even at the guaranteed interest rate and current mortality, UL is better because of the flexibility. Really a no-brainer right now.
Personally, I don't care for ROP term except in very high interest rate environments. In high interest rate environments, the high interest rate allows for lower ROP premiums (and effectively "guarantees" the high interest rate). But even then the client has to keep the policy for the full term, and the lack of flexibility is problematic. You have to make sure the client understands this risk.
I'm not a big ROP guy but do use it where it fits. If I'm buying 30yr ROP for a younger client (30s) I would be surprised if the UL would even come close for the same premium/DB...it would likely lapse (even on the current side) long before year 30. Maybe you're using your idea with a different demographic but this is where it mostly comes up for me.
Also, most of the ROP term policies that we use (Trans, Pru, ING etc.) allow for cash surrenders and RdPu options long before the end of the term.
I like flexibility too but as with most term sales, we're normally trying to max the DB for a specific need (income replacement, debt repayment, etc.) so I'm not seeing how a permanent product can compete for that specific reason.