requirements for queueing

In transformer_transform_perform there is the comment:
"@todo: test priority. queue if necessary?? need a way to communicate that it should be queued."
This will be something I have need for. Just dumping my thoughts here.

• A queued transforms/macros. Maybe everything should be queued. A new table I assume.
• The queue table should grow, successful tranforms should be noted as such (rather than the record removed). hook_cron removing old records.
• The queue should have fields like "# of failures", "last execution time", "error message"... to record issues.
• We leave it up to the module to ask if the transform has occurred. A module should be able to query transformer with a file name and find out whether the transform is stilled queued (and has failed 0,1,...N times).
• Need a function that can check system resources (??) and determine whether or not to kick off additional transforms. This is out of my league.