If all shibes just dump all their free TIPS then more investments by the TIPS community will be needed to stay at the same price level. This in fact would decrease the value of all coins held by now.
How can we know dogeminers won't dump them all?
That is just going to be like anything else. Not to state the obvious here, but I am going to anyways, if there is no one to buy them then there is not going to be anyone to dump them. That said, you would have to convince them to hang onto the coins for future value, once again not to state the obvious. I am currently mining both coins, and I am just banking them all.
I personally would love to see a reduction to the total number of coins available.