11th should bring back:
>Templates
>Old AP
>Tank facings and AVs
>Psychic disciplines
>Psychic tests and perils of the warp
>Warlord traits
>Armoury
>Point costs
>Old wound allocation
>WS chart
>Additive S/T chart instead of multiplicative
>Detachments as armylists (ie, detachments should have their own restricted/expanded list of units)
>Cover saves
>4th edition terrain rules (dangerous, difficult, impassable, area)
>No stratagems
11th should copy from 30k 3.0:
>Morale
>Flyers
>FOC
>How characters attach to units
>USRs
11th should keep from 10th:
>Mission design
>Pre-established terrain placements (though they should be more generic and varied, not just ruins)
>Detachments (with some tweaks)
>Crusade (especially at the quality of Armageddon)