Q: Are there plans to allow Sonos access to iTunes match library without having to subscribe to Apple Music?

No one here can say. We are users like yourself.

See

Apple Support Communities Terms of Use

"Speculations or rumors about unannounced products are not permitted."

You could in meantime check here

Using Apple Music on Sonos - Apple Support

Or here

https://sonos.custhelp.com/app/answers/detail/a_id/2978/kw/Beta/session/L3RpbWUv MTQ0ODkyODY3My9zaWQvTEtpRkNRQ20%3D#var_1

Or contact Apple with product feedback here

Apple Product Feedback

"Apple strives to bring the best personal computing experience to students, educators, creative professionals and consumers around the world through its innovative hardware, software and Internet offerings. Apple welcomes your feedback on its products. Begin by selecting a product below."

http://www.apple.com/feedback/