My (admittedly limited) experience w/ Abbaye so far has shown that it's a pretty neutral yeast, as far as Belgians go. The batch I'm fermenting right now with it had it pitched at 17.5C and I've let it free rise to 23.5C. It's throwing some mild esters--pears, apples--and a ton of sulfur, which should clean up. There are also some mild phenols, but nothing too sharp or spicy. And like you said, it can definitely handle the alcohol, and you know it won't underattenuate (it's a real beast).
I'd think for an Imperial Porter some mild esters wouldn't be the end of the world, though you'd probably want to avoid too many spicy/peppery notes. So I'd pitch/aerate properly and ferment on the high end of things (folks who have fermented in the low-to-mid-60F-range have commented that it's very spicy/phenolic around there).
In conclusion, I think it'd be an interesting experiment, and as long as you have the ability to control your temperature pretty closely and don't let it ferment too cold I think it might be a pretty interesting beer.
