This might be harder than I could imagine (or maybe simpler). Let's say I have all of my content (1,000-plus entries) in Blog 1 with its own set of templates and design. Is it possible to mirror the entries, without having to duplicate them, to Blog 2 that uses a completely different design?
This is an older blog, still running MT 3.35
Reported on Movable Type 3.x
Give this a shot. It's a plugin for 3.x, but a feature for 4.X: http://www.apperceptive.com/plugins/multiblog/
How different are the two designs?
It may be possible by having a reference to the stylesheet via a relative path.
Both domains point to the same content using a common layout with a different stylesheet for each domain that fixes the design.
They would be pretty different, even pulling a limited amount of content than the original.
There's nothing stopping you having both sets of templates in the same blog then making their publish paths a sub-dir. MT should be able to work out the correct links as long as you've defined it all well enough in your archive mappings.
Other option could be a SQL command setup on a cron job.
I agree with Richard. If you specifically don't want to have duplicates, you should just make a second set of templates in the same blog that publish to a different directory. The second blog would be unnecessary in this case make publishing archives much more difficult.
Excellent recommendation. Hadn't thought of it that way. Thanks!