AFAICR, the last news from the Sibelius stables was that they've pretty much moved on to the PC and Mac market exclusively. From fairly recent telephone conversations on an unrelated matter, it seems there's basically one or two people at Sib HQ who deal with re-issuing broken Sib7 install discs.
The company as a whole seems fairly content not to bother actually making their software anything special anymore, as they're getting loads of money putting it on every secondary school Music PC in the country.
I recall their original reason for leaving the RO market was that they were looking at rewriting in C, and at the time, the Acorn C library was horrendous.
It's a real shame, as Sib7 remains intuitive, and (barring the occasional editing bug) a pleasure to use. The windows (and, I assume, Mac) version is far less user friendly.
I have yet to hear from anyone willing to take up my challenge: Me on Sib7, them on Sib for win or mac. 1 page of music, however complex you like. I'd stake quite a bit on a faster time, and a nicer end result.