In my ignorant opinion, there is very good sintesizers in linux, but no open source High Quality Orchestal Library (better than Sonatina. like Hollywood Strings, for instance). This may be because such a thing requires a huge investement in money, facilities, musicians, technicians, etc that no small team can do, opposite to sinthesizers. Recently I read about the succesful fundraising campaign Musescore launched in their Open Goldberg Variations Project (http://musescore.org/en/node/9622). With a goal of 15.000 USD, the fundraising has got to 23.000 USD.
So I was thinking that an appropiate Kickstarter (or similar) campaing to hire the studio, the technicians and the orchestra to record and produce an High Quality free-software orchestral sample library (in gig, sf2, sfz?), could raise more than that. Think that it would be something every digital musician needs sooner or later, and it would interest not only linux musicians, but windows and mac ones too. Everyone, in fact. I cernainly would give some money to it.
I have absolutely no idea how expensive that could be. But it would be nice to see it happen!