If we talk about H/W Specs, everything that is there in N900 with a bigger, 4-5 inch SUPER AMOLED multi-touch screen that should

1) Have scratch resistant coating
2) Good display under sunlight
3) Proof from fingerprints
4) A Dual CPU with good Graphics for gaming (Something similar to what LG Optimus 2X have).
5) Minimum 8MP camera with Autofocus and Carl Zesis optics. The camera should have
a) Touch Focus
b) Face Detection
c) Smile detection
b) Should be able to record HD Videos (1080)

6) And above all else, it should be Good in looks, I find N8 and E7 Ugly. N900 has got a beautiful look. So if a bigger cousine of N900 having all these specs, even if it weighs more than 200 LBS, it would'nt be a concern for me I can invest nearly 1000$ for such a dream device

In terms of S/W there is no limit