I would want, coming from a SP2...
1. Screen Size- Same as SP3. I think 12in is fine. Hows about a thinner border and a easy way to kill the windows flag on the tablet face.
2. No bloatware/freeware- Give it on a thumbdrive or as a downloadable link to those that want it.
3. Screen Resolution- Same as SP3. As long as the dot pitch is high enough so text is smooth and windows can SUPPORT DPI adjustment as well as a Apple product, I'm fine. I want to run my Photoshop it high resolution, but have my menus readable please.
4. Weight and size- Same is ok. A bit heavier with larger battery. I don't care if Broadwell/Haswell can be used without a fan. Make it work so 80% what a person does, doesn't need it. But the 20% work that makes the CPU/GPU hit 100% has a fan to keep it cooler. NOT hot, but warm to touch is fine. I wouldn't care if I could hear the fan that much if I knew I could keep it on my lap or hold it without feeling like my fingers are going to get burned like my SP2.
5. Ports- At lease 2 USB 3.0 and one USB-C if possible. With higher wattage to allow USB fast charging of cellphones.
6. CPU/MEMORY/STORAGE- Minimum i5/i7 Haswell, or Broadwell if possible./8GB (C'mon,memory is cheap now)/128GB SSD/
7. Display- Same or better than the one in the SP3.
8. Exta hardware- a Long charging cord. I would rather have a thinner ac adapter than a thicker (square) brick. Easier to put in a bag.
Pen- At least something that works as well as Wacom pens. AND works to ALL corners of the display!
9. Price- $1500 on the high end. BUT include the damn keyboard. You want people to NOT buy Apple? Give more at a cheaper price. Once they see how good it is, they'll continue to buy the product.
10. Battery life - At least 8 hours of web use or word processing. Using 60% brightness. Or watching a HD SSD stored movie for up to 6hrs. Enough to last a long flight.