If they intend to use non after burning engines then it would be purely subsonic only... which would mean why no use the engines currently being used... I doubt the difference in performance would be enormous and it would be a useful way of using these engines in current Su-57s that are to be replaced as soon as the new engine is deemed to be ready.
What do you mean by "engines being currently used"? Izd. 117 is currently being used, but they need a version w/o AB so that needs to be created specifically for the Okhotnik. The izd. 117 has been taken to serial production and we hear about a new engine for the Flankers, so maybe it is going to be the baseline engine for the VKS. Of course it makes sense to use it rather than older AL-31F engines, it has a longer lifetime and much better performance, and the industrial base in Russia needs to move forward from engines created 40 years ago.