The Hydroid rework looks really fun and I'm excited to try him it out! That said, one thing I wish he was getting with it is some lore so I can feel invested in him. Moreover, I think a bit more pomp and circumstance to a rework would get more people interested in trying out that warframe. So with that in mind, here are some additions that I think would help make reworks feel more like events!
1. Reworked warframes should get a Leverian or some lore added to their codex entry
A Leverian would really sell the "eventness" of a rework, especially if we could find Prex cards in them like the others. That being said, if a Leverian isn't feasible, a nice alternative would be to add lore to the warframe's codex entry, similar to Mag or Rhino Prime.
2. Reworked warframes should be featured in the new Update History Screen
This screen shown off in the dev workshop is a fantastic addition and a perfect means to show off a warframe rework! I think a section that shows how to acquire the warframe alongside, say, directing them to a new Leverian or codex lore entry, would really be helpful in getting people to try the rework, especially for newer players who might not know how to get them.
3. Reworked warframes should get new skins
Hydroid's deluxe skin is incredible and I'll be using it a ton when his rework comes out. That said... I also bought that years ago when it came out. Since reworks take a lot of dev time, I think it makes sense for new deluxe skins, bundles, and Tennogen to come out alongside a rework.
And those are my suggestions, let me know what you think!