Average and Standard Deviation using Measures as arguments

You should be able to do this with AVERAGEX and STDEVX.S. These functions ignore blanks but include zeroes.

This might work:

AVERAGEX (
    {
        [Month -2],
        [Month -1],
        [Current Month],
        [Month +1],
        [Month +2],
        [Month +3]
    },
    [Value]
)

but you probably don't need separate measures for each month offset when something more like this should work:

AVERAGEX (
    GENERATESERIES ( -2, 3 ),
    CALCULATE ( [Measure], DATEADD ( 'Date'[Date], [Value], MONTH ) )
)

You could switch between them.

AVERAGEX (
    GENERATESERIES ( -2, 3 ),
    VAR _i = [Value]
    RETURN
        IF (
            _i <= 0,
            CALCULATE ( [SumCurrent], DATEADD ( 'Date'[Date], _i, MONTH ) ),
            CALCULATE ( [SumFuture],  DATEADD ( 'Date'[Date], _i, MONTH ) )
        )
)