I've got a fix, even for those who don't have hotspot (like me) who want to get the ipad and iphone talking over bluetooth again.
Earlier I said that when I got my 4s, the problem was solved. It was not. I was just connecting via wifi, but I wanted bluetooth back.
Here is how I got it back without hotspot.
1. Launch keynote on one device and the remote on the other as you normall would.
2. Find another app that bluetooth links ipad and iphone (I used 'pictransfer light'). Install on both devices and launch on both devices. Follow the promt to get a bluetooth sync.
3. Double push the home button both devices to pull up the multi-tasking and open keynote and keynote remote on the relevant devices.
4. In keynote, go to settings; advances; remote. You should now be able to get the remote to link (you may, on the device running the remote, need to hit settings and then 'new keynote link'.
Once I launched pictransfer, the bluetooth logo was blue on both devices the whole time I ran through the other steps. I suspect that that was also the point of using the hotspot service.
Also noteworthy: I am yet to try this 'in the field'. For all I know, this won't keep a connection for as long as one might need. I'll find out on Thursday when I rely on the remote for 90min. On the positive side, I was able to keep the connection even when I double clicked home and closed pictransfer while leaving keynote and keynote remote open...