I absolutely agree that non-vibrato strings would be a welcome feature. Especially for harmonics. Who ever heard of harmonics played with vibrato?!

You can certainly make a feature request of this, but my perspective, GPO and GPO5 are affordable products that put an orchestra at your fingertips. But they are both old pieces of software with old programming, there are newer, improved (IMHO) sample libraries out there which fixes the vibrato issue and includes many other improvements over GPO.

If you're curious, look up NotePerformer.

I didn't know what others were thinking, but it was helpful to see some of the comments. I am a string player, and I feel the vibrato is not realistic. We use different speeds/intensities/amounts of vibrato in the real world. And sometimes, as others mention, we delay vibrato. In a real string section, people don't really change their vibrato. Everyone adjusts it to the music from training and experience. Unless a composer is specifically calling for no vibrato, there would be some vibrato. In order to get "less" vibrato, I use "section strings", but given the single string vibrato options in Finale, I don't understand why "section strings" would sound vibrato-less. Also, section strings makes it sound like more instruments are present. 

I didn't know what others were thinking, but it was helpful to see some of the comments. I am a string player, and I feel the vibrato is not realistic. We use different speeds/intensities/amounts of vibrato in the real world. And sometimes, as others mention, we delay vibrato. In a real string section, people don't really change their vibrato. Everyone adjusts it to the music from training and experience. Unless a composer is specifically calling for no vibrato, there would be some vibrato. In order to get "less" vibrato, I use "section strings", but given the single string vibrato options in Finale, I don't understand why "section strings" would sound vibrato-less. Also, section strings makes it sound like more instruments are present, which is a problem.