They weren't rares when Jagex first implemented them, they're known as rares now because of how long its been since those events. I think they should do it the old way, hence the name "Oldschool RuneScape".. I wasn't around back before 2005 so I never obtained a party hat, had a few santas and masks and such, but they should be introduced accordingly, like Santas on christmas, H'ween masks on halloween, etc.. Imo it'd be nice to keep the tradeables still tradeable and let time have its toll on the 'rares'. I wouldn't go so far as to give every Old player a rare, that would be silly.
Also, some people do not do combat skills, personal preference, I do so I am not part of that bunch, but if they were to have to kill high level monsters.. That would not be fair too. Same goes for people who don't do clue scrolls, or non-combats.
It's nice that they're bringing it back, I'll be greatfull if I get bunny ears and a sythe + rubber chicken, and maybe my first party hat.. Don't even mind if its just one.