From what I gather they could make equipping them while PVP tagged impossible, but I'm not sure about removing them if you become PVP tagged. If added back I'd like to see them removed if you become PVP tagged (into your inventory). If someone planning to use an elytra as a form of escape from PVP, I feel like they might also use it to fly into the person's base they are raiding. If they can be shot out of the sky if they just fly in a straight line and don't bother to avoid arrows then I feel it should be fairly balanced. If they make it so you can't use it when you're PVP tagged, if I raider wants to escape with it they would still have to avoid the defenders for the 30 seconds it takes to get PVP inactive again, then use the elytra to escape. Seems balanced. Note - I do want to avoid a raider stopping mid fight and managing to equip and elytra and just rocket away. That seems a bit unfair. But if a raider manages to get away from the defenders for long enough to go PVP inactive, they should be able to choose if they want to /tp out or elytra out. I feel if they're elytra'ing out they're just getting out to hide and reset and then raid some more.
When I first used elytras and rockets it was to fly around the world and visit builds I saw on the dynamic map that I thought looked cool but didn't want to run all the way there. So I do see the purpose for elytras outside of PVP, since that's what I used them for first. (I have never used elytras in PVP, so I'm looking at that aspect from the outside and trying to suggest the most balanced approach)
If you aren't wearing the elytra you can't fly.. so just have it become unequipped while combat tagged
That is true. If you are wearing it and travel to a restricted world its just put in your inventory. That could work