The addition of a method for registering an IIcon for the Turtle Upgrade would be most useful; Yes I know this is possible through registering for texture stitch events and the such from Forge, but it makes more sense to me for it to be implemented once at your end as opposed to each time in any peripheral mod that needs it.

Basically adding void registerUpgradeIcons(IIconRegister registry); to ITurtleUpgrade would accompany IIcon getIcon(ITurtleAccess turtle, TurtleSide side); well.