Last year the Bayreuth Opera house was added to the list. I looked into visiting it then but didn't. With all the holidays coming up I am making plans for weekend getaways, and just found out the Bayruth opera is closed until further notice! URL
Anyone knows a bit more about this?

We are scheduled to be there in August for the Festspiele (a different opera house of course!) so I too was disappointed to discover that the Margravial opera house is closed.
It appears however that, from this May there is intended to be an exhibition and a chance to see the work in progress
http://www.bayreuth.de/tourism/welcome_to_bayreuth/sights_364.html

If you are in Bayreuth after this exhibition is scheduled to open I would be very interested to know if it IS in fact there!!

The renovation started in November 2012 and will last several years. According to http://www.bayreuth.de/sehenswuerdigkeiten/markgraefliches_opernhaus_778.html from May you can see an exibition and take a look at the (wrapped) opera from one of the boxes.

I would strongly suggest you not to visit the opera until the work is finished. Especially not on a weekend getaway. I managed to see the opera before they started the renovation and it's truly unique. According to their website you will mainly see a construction site. The decorated walls will be covered.

The Opera House will be closed at least until 2016. I've visited it in 2011, it's really magnificent. Though the interior currently looks rather dark and gloomy. I could have a short glimpse of the result of the renovation works, in a small area the renovation was tested, and it looked great.
The renovation aims to restore the opera in the original appearance from 1748. Originally, the light green paintings were bright and glamorous. In the 1930s parts of the walls have been overpainted in dark green, and in the 1950s there was an ample use of oily wood preservatives which additionally darkened and impaired the paintings. And also modifications of the stage from the 1930s will be removed. Finally, air conditioning and fire protection required by Unesco/ICOMOS will be implemented.

This website gives a good impression of the interior:
http://www.schloesser-bayern.com/fileadmin/sites/schlbay/pano/ofra/bayr-opera/pano-sv .html?pano=fr/vor-oper/pano.xml