I don't think the profitability now will last long , it will decrease again until it reaches the what i call mining support point which is $1/card seems like the avarege electricity prices worldwide keep this support point from getting lower , the only thing that can break this $1/card/day is newer hardware getting out to the market...
it depend, last time mining was far less profitable not because there are many gpu, but because all coins were dumped, the diff can't keep with the value if investors go serious, like they are doing now
and this is nothing, if for example 1B people invest in crypto, you would see crazy high value, and no matter how many rig you buy it would not compete whit the pump that would happen
I think that will be a slow process. The difficulty will rise as the price increases.