New attraction coming soon - What could it be?

We are very excited to be organizing a special day for our friends and fans! The museum will be open only for you during this afternoon, March 13. Tickets will be released for pre–purchase during January. The day will include:
* We will reveal our biggest attraction since opening!
* A never before exhibited costume from 1973.
* Preview and pre-purchase of fine art photos never exhibited before, by Torbjörn Calvero.
* A unique walk through inside the Polar Studio, with guide.
* Competition; one happy person will also get to sing in a microphone in the studio.
* Get your own ABBA The Museum backstage pass/Friends Card. The card will give you special offers and discounts.
* Premiere of our curator’s audio guide. An ABBA The Museum tour in depth.
*Mingle and drinks

The day at the museum will start around 3 p.m but all visitors are welcome earlier as well. We will be able to offer good pricing on hotels nearby, such as Melody Hotel & Hasselbacken Scandic. Keep posted for updates. A warm welcome and we hope to see you here!

I'm sure everyone is just as excited for this as I am (even though I can't be there).  The new attraction sounds so exciting and I can't figure out what it could be.  However, the never before exhibited costume from 1973 must be some outfit from 1973 (duh).

I'm wondering could these be the outfits?  I don't really see them a costumes but more like fancy clothes that they wore.  (I think Frida did an excellent job making the top for Agnetha.  ;) )

 Or possibly the jumpsuits that Frida and Inger are wearing at this performance.  

There are, of course, these outfits that ABBA wore several times.  :D  I would like to see these on display someday.  Same for the velvet jumpsuits from 1975/76....

I bet it's going to be these last outfits that I just put images of.  I can't wait to find out though, and when it happens, I can't wait to see (via internet, of course)!  :D