I can't get behind Grixis Tempo for the following reasons:

I don't think 8 rather fragile wincons are enough.

Delver is fragile because of its low toughness.

Tombstalker is fragile because its needs BB and some cards in the yard and can easily be sworded or beaten/outclassed by life total advantage or some other board presence that was achieved earlier.

If you compare that to RUG tempo which plays 12 creatures (4 of them having shroud), just the addition of discard cannot make up for the loss of threat density.

Comparing to TA, I feel the deck wins red reach, but looses it's most important defense with Goyf & Deed.