The SACD including the 2nd quad mix that was on "Boxed" has been one of those "facts" I've known for so long, I have to dig for the origin.
There is much discussion about different mixes on the poll thread of the SACD - although a lot of confusion and speculation, but page 3 Owen states directly that the SACD is the same as the Boxed mix.
HiRez Poll - Oldfield, Mike - TUBULAR BELLS [SACD]
Then there's this thread where I flat out asked what was what, and the answer was that the SACD includes the Boxed quad mix
"Tubular Bells" SACD Features '70s Quad Mix
Of course both of these come under a saying I am so fond of, "I read it on the internet, it must be true"
I have the Boxed CD and the SACD, although it's been a long time since I've played the Boxed CD or ran it through a decoder of any kind - although on quick review both have the same Narrated ending while the CD4/Q8 mix doesn't have narration at the ending.
So, based on the SDE announcement saying it includes the 1975 quad mix, and the Boxed mix coming out in 1975 with the US CD4/Q8 coming out in 1973 according to discogs, and the other observations I've laid out here, I believe the SACD includes the 1975 boxed quad mix, and that the bluray will also include this.
But, I could be wrong, and I suppose we'll find out what exactly is on the bluray when we receive them.