So if I transfer 100k from my MR to my wife's Delta account, will get: 100K delta miles and 40K MR points rebated. Cost: $70

Then transfer 100K delta to my own account for 100% bonus = 200k delta miles for $1100.

Then transfer redeem for GC: 200k = $1800 in GC with 2k remaining

SO:
Cost
60K (after 40K rebate)
$1170 (charge to MR card)


Benefit:
$1800 Amex GC
2k delta miles

Even if you value MR at 1%, this is a decent churn if doing for points alone.