Hi, First of all, i have to apologize for being away from computer since few days. This was easter days. Happy easter days :D
About proprietary backends. They have to support SANE, but SANE has not to support those backends. Actually, as Allan said, nothing will be break. And it's up to the proprietary backend to provide its own HAL callout. The discussion is not about patching e.g. XSane to use HAL, but rather to allow parallel unified device naming in SANE backends. This will allow a HAL callout to compute mostly working SANE device name in order HAL addon to open a device on plug and monitor its sensors, and much more. Regards, ?tienne.