My thought is that you would just get a suspension corrected fork and leave the geometry the same. Maybe a little less trail than most mountain bike forks. Modern mountain bikes have slack head angles and high trail for self-centering of the steering.

I am building a similar bike, but I decided I will always have a rigid fork. I'm of medium build, and a 29er with suspension fork puts the top of the head tube higher than I want on a road bike.