"I'm actually hoping Eby can come up with some kind of solution, at least enough of one to make manned Mars flight possible... otherwise I've got a massive re-write to do..."
Such confidence in Mark.
Well, kinda off topic, but I thought of it reading your post:
I was thinking that Mars might make a nice location to intentionally steer impactors into- not specifically to terraform- but simply a convenient place to put asteriods which have minable resources in them. The idea being you would steer these objects so that they impact with the least velocity- so they don't "nuke" but they can explode on the surface- it makes easier extracting the ore.
Mars has various advantages in this regard (in comparison to the Moon).
First Mars has more rocks to choose from (requiring the least alteration of delta-v).
At Mars distance there is a higher density of rocks per cubic area of space. It's distance from the Sun means less delta-v required to change inclination of the rocks and there is more area (volume/space {bigger sphere})
Second you have that thin atmosphere [that's the one, Mark is always praising:]
This allows you to aerobrake your impactor- like MGS did- spiraling it, but continue aerobraking until it impacts.
Third nobody lives there- and anybody who chooses to, could live fairly deep underground. Nobody live on the Moon but it has a rather densely populated planet fairly close.
Fourth it will add atmosphere (don't want atmosphere on the Moon).
Finally, probably after about 100 years (or less) all minable rocks will be cleared from the area- maybe then Martian government can contract out for all rocks to be impacted. This activity should increase global temperature and add atmosphere, so people could perhaps use Mars as a ski resort.
-gb [A slightly different vision]