There's already been a great response to my post last night (see the comments to previous entry). Greg suggested his aggregator Blogdigger could be included in this - I agree! Matt and Andrew also posted very thoughtful responses.
Here's some of my feedback (copied from the comments - I must get these enabled inline...):
Overnight while pondering my post (which I regard as just a 'starter for 10' btw, not a final solution by any means), I did conclude that KC essentially already does what I describe - polls registered RSS feeds with ENT in them and aggregates them. It would be great if TE also had that functionality.
It's the client ping that I think is unnecessary and possibly holding back community uptake - with TE the ping is a manual process for the blogger, and with KC you need to install an add-on tool to enable the pinging. Both require too much manual effort for the blogger (IMHO of course). eg Bloglines does all its aggregation automatically (every hour I think), with no pinging required from the blogger.
Although Andrew I take your point about bandwidth utilization. But if Bloglines (and Blogdigger) can do it, why not KC and TE?