It would be interesting. I'm not familiar with 2.5 nor the potential of 2.5.
I do however think if you are going for power and piston, LSx is a far better choice. I've talked to Hinson in the past and I know they were interested in doing the LSx in RX8.. They asked me if I was interested.. but I'm not really looking for 400+ NA power and my daily being out of commission for 3-6 months

Also, I think if I want pistons, then i would go buy a piston car and save me some time and headache
I've seen people do LSx in an FD and some after the conversion, just goes out and buys the real thing.. To be honest, it might be cheaper these days.