I have both a cellular iPad Mini and iPhone. If I try to enable instant hotspot from my Macbook (Yosemite Beta 3) with either device locked I do not see the option in the WiFi dropdown. However, if I wake one of the devices, unlock it, and then go back to WiFi it shows up. I'm sure this has to be a bug as it defeats the purpose of hands free enable.
iPhone to iPad and iPad to iPhone works just fine with the opposite device locked so it appears to be limited to my Macbook.
Oddly enough, if I do the following it also works:
1. Open WiFi dropdown on macbook
2. Go to iPad Mini and search for WiFi
3. iPhone personal hotspot appears
4. iPhone personal hotspot now instantly appears on macbook too - don't even have to close and re-open like I do with the wake method above
iPhone to iPad and iPad to iPhone works just fine with the opposite device locked so it appears to be limited to my Macbook.
Oddly enough, if I do the following it also works:
1. Open WiFi dropdown on macbook
2. Go to iPad Mini and search for WiFi
3. iPhone personal hotspot appears
4. iPhone personal hotspot now instantly appears on macbook too - don't even have to close and re-open like I do with the wake method above