Not going to happen. Dropbox provides compiled x86 (Intel) binaries.
Not sure why that is a valid reason for it not to happen. I'm sure there is some way for someone to make this happen
It's not as easy as just cross-compiling a package for the sparc processor. dropbox for Linux is a plugin for the nautilus file manager, thus it requires the GNOME Desktop. Dropbox offers a nice Python development kit though. This brings everything you need for your own dropbox client implementation which on ReadyNAS would need to be a web application of course. Find someone who can write web applications in Python and they should be able to produce something working very quickly.
Personally I'll keep an eye on OwnCloud. I already got version 3 working on ReadyNAS, version 4 is already out. It's not quite stable yet and lacks some features but looks very promising and is very actively developed. It's a PHP application with mysql Database backend. ReadyNAS already comes with apache webserver and mysql database and PHP 5.3 is available as community addon by WhoCares?, albeit not for free.
