What would you include in each Album Boxsets

Neither. Unless if it's "ABBAtakes" for which it, hypothetically speaking, composes of most unreleased tracks; some are from "ABBA Undeleted" but shown in full glory so others can perceive that it's not a medley, it is an individual song that's in the early stage of being a polished individual song, and some outtakes and songs have not been released, only circulated as a bootleg before.

There's absolutely no point of having a box set of one album, unless if it happens to be significant because it's waste of time and money if no proper materials are provided in a way that would give us a bit of information on how an album is significant in some ways. If every album on its discography had its accompanying box sets, very few would be enthusiastic to get some. Some would accuse Polar Music of being desperate for more money with recycled ideas. And that's not good. Some just don't think it's their cup of tea because it's the same thing over and over again.

I'd rather take the 'Deluxe Edition' game approach a bit further than what Polar Music did, although they would rarely think outside the box:

For Waterloo, I'd like to include the outtakes from the Metronome Studios sessions of Waterloo, packaged in vinyl, digital multitrack stems of the Eurovision hit swooner "Waterloo" available for karaoke, "do it yourself remastering" and remixing. (Well, it would be in a remixing contest.. think about it, not really a bad idea. It's pretty much like what Mike Oldfield and the Beach Boys did a few years back)
For ABBA; a BBC documentary of "Mamma Mia" if possible.
For The Album; a video of how Benny and Björn composes "The Girl with the Golden Hair", and, rather, get the full Australian concert, and provide a few multicamera excerpts...(e.g. Benny-cam, Agnetha-cam, Rutger-cam)
For Voulez-Vous; go crazy with the multitrack stems of selected tracks (Voulez-Vous, As Good as New, If It Wasn't For The Night, Gimme Gimme Gimme, etc.) so others can remix it for the sake of it. Benny and Björn have been living under a rock for enough of a year.
For Super Trouper; Ditto, as stated in Waterloo, because I couldn't think of any
For The Visitors; The story behind Frida's hair and unreleased photos of her cutting her hair, so to uncover the mystery, (book, DVD, documentary, whatever media it's in) and a remixed version of The Visitors (if any digital multi-tracks in the tapes can be found) where the vocals are prominent and have no phasing effects

I don't think there's a need for any more boxsets unless they include something completely new. Frida's box was nice but not exactly groundbreaking, was it? Jonathan's ideas are good, I especially like the vision of Deluxe Editions including second disc with early versions, alternate takes and mixes and unreleased tracks. But we all know it will hardly happen. As for the Australian concert.. it should be released on its own and I still believe we will get it one day, at least on CD.