We'd like to have a technique for getting at the DOM in process. In this case, the performance degrades exponentially. Glen Gordon complained that the performance hit caused lots of problems. We've been trying to get Rob Sinclair and Rob Rylea involved. I can't offer much at this point.
All systems have the notion of a registry.
It would be possible for user agents to launch assistive technologies and communicate with them in-process. Very very fast. Often, in timing, there is information in events. Accesses in-process were on the order of tenths of nanoseconds. COM is smart, so in-process, doesn't do mappings that take time.