Interesting. One thing to consider is support for (or non-exclusion of) soft keyboards. In a tabletop setup, you could have multiple keyboards, each with a different focus (or list of subscribers). Same thing for mouse input. There could be systems with more than one mouse or, more likely, multi-touch input. I've been using Squeak / Pharo for fairly novel devices for some time and having the flexibility to augment the events, etc. has been really useful.

Cheers,

Jeff