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Using CGI to rejuvenate, or de-age an actor could work much better than the effects we have seen thus far which are still in their infancy - Peter Cushing does look amazing despite having been dead for over 20 years, but the effect is far from complete.

Another issue is the actor's voices, which have aged a great deal and would not match any such CGI trickery. Alien Isolation is a perfect example, with the Nostromo DLC (I forget its name) featuring recently recorded audio from the original cast that didn't quite match the youthful appearance of the characters.

It costs a lot of money to do a very good job... the Photo of Ripley above is realistic... but its not good enough for a Movie where other cast members are actual Actors etc.

Why Terminator Gynisis  so much was spent on Schwarzenegger Character CGI and not on the other returning Characters from the Original movie... due to costs.

Why Tarken looked up to the Part in Rogue One... but Leia did not look so good..

A Alien 5 with little screen time to a younger Ripley could work with the effort they put on Tarken in Rogue One... but for playing a Character with more screen time... i feel even the Tarken CGI is not up to scratch.

i think in 20 years time we would be at the level to pull it off... and i expect more Re-boots of movies then.. where they would CGI the Original and even long dead Actors and use voice-a-likes.....  so could prove a time that could effect paid Actors in future...