By the time you get the new card, you will mine the same amount with the same price as the difficulty will be much higher.
You have a valid point there. By the time they come out and a ginny pig spends $200 to find out if it will mine ETH and we get word of it, it's quite possible my 3,000 MH/s from 100 x MSI 390's will have mined approximately $10,000 worth of ETH at current difficulty, block time and price of ETH.
That's $10,000 towards a $34,000 to $35,000 investment. That investment could be paid off in 4 months.
I'm an ignoramus as to how ETH works. Any idea who or what determines when ETH changes from POW to POS? Of course, I could research to find out for myself. However, if someone knows the answer, I would appreciate the info.
I was researching this topic earlier this year and find this link best to explain POS/Casper and Life after POW.