If we look at the process right now, there are two threads: one is doing enwiki, the other hewiki. The enwiki thread isn't even to pages-articles yet, and will run for weeks. The hewiki dump will complete in a day or so, but then next on deck is dewiki, which takes at least a week.
So with things running now, it will be a week or two before any other projects get anything.
As you say, it would be easy to make threads limited to smaller projects; I'd suggest adding an option (-small or something) that just has the code skip [en, de, zh, he ...]wiki when looking for the least-recently completed task. The code list should be 10-15 of the biggest 'pedias, and possibly commons. Then start two small threads, and everything should go well?
Is it necessary to skip the 10 biggest? I think skipping just the top 3 would be a massive help.