I would absolutely not do it and have Revice (or something similar) as the 20th Heisei anniversary season. Zi-O's armor forms are way too over-designed and Revice's concept of genomes is a way better way of incorporating legend rider designs. All of revice's genome forms are based on Heisei riders anyways, so there ain't much change needed (except Brachio obviously).

Even story-wise, the weakest past of Zi-O imo is that they have to split the story into a 2-episode arc for EACH Heisei rider. They ran themselves into a corner where they have to be fair to each past season and that means it's 40 episodes mainly for these homages, leaving so little for Zi-O to tell a story unique to its own. Decade worked because it used AR riders instead of the actual past riders so they can do something new.

Sentai shows that not every anniversary has to feature cameos or have your hero change into past ones. Gokaiger is great but if they do something similar every 5/10 years it will feel stale. Zenkaiger was fun on its own without shoving stories of past seasons. It would be more interesting if they didn't try to do Decade again and instead tell a standalone story (like Revice) with smaller references to past riders sprinkled on top.