I kinda hope they give us cards made in the spirit of older cards, but also keeping in mind how modern cards are designed. Most Base Set-era stuff is horribly weak by today's standards, while a lot of the best utility Pokemon from the DPP era would be Pokemon-EX these days, and would likely be overpowered as non-EX Pokemon. A set or series of sets based on this concept could be great.
That being said, I honestly don't want them reusing MECHANICS from the past that are no longer in use. Bringing things like Pokemon LEGEND or Pokemon Lv.X back for a single set/mini-series is bad for the game, and potentially confusing for a significant portion of the casual playerbase.
I'd be interested in seeing what cards people would like to see a card being based off, honestly. (Not necessarily a direct port, of course, not like we'd get something like Jungle Mr. Mime or Neo Genesis Cleffa in its original state, but we could very well get cards based on them.) I'd personally like to see how they'd handle cards based on things like Jungle Mr. Mime, Electrode Prime or Stormfront Machamp.