Then there could be thousands of people who never get the full 100% of the file. Particularly if only one person starts out sharing a specific file of their own.

I guess there's always plusses & negatives for such options as that, including specific speeds or % of speeds for particular sharers.

I'd like to see something like many torrent programs where users can make some limitations for leeches; eg: share ratio.
Not totally blocking leeches however, just giving a lower priority in some respect.

Azareus slows your downloading speed if your share ratio is less than 0.75, and slows it even more the lower your share ratio is. My share ratio is always well over one nowadays. My LW share ratio (if there was one) would also be well over one if there was such a thing to have recorded my share history. (ie: above 1.0 means you have shared more than downloading, less than 1.0 means you have downloaded more than uploaded.)