What is the enhancement in mind? How should it look and feel?
Would like to request support for Deathknight presences as a tag.

Please provide any additional information below.

What I did to get it working is a quick hack added to Auras.lua as follows:

local function DKStance(unit)
    local _, c = UnitClass(unit)
    if c ~= "DEATHKNIGHT" then
        return nil
    end
    local icon, name, blood, frost, unholy
    icon, name, blood = GetShapeshiftFormInfo(1)
    icon, name, frost = GetShapeshiftFormInfo(2)
    icon, name, unholy = GetShapeshiftFormInfo(3)
    if blood then
        return "Blood Presence"
    elseif frost then
        return "Frost Presence"
    elseif unholy then
        return "Unholy Presence"
    end
    return nil
end

DogTag:AddTag("Unit", "DKStance", {
    code = DKStance,
    arg = {
        'unit', 'string;undef', 'player'
    },
    ret = "string;nil",
    events = "UPDATE_SHAPESHIFT_FORM",
    doc = L["Return the DK stance form the unit is in if unit is a DK"],
    example = ('[DKStance] => %q; [DKStance] => %q; [DKStance] => ""'):format("Blood Presence", "Frost Presence"),
    category = L["Auras"]
})

And I am sure the same thing would be possible to make for warrior stances as well