Those who have huge holdings, will not need pumpin anymore. They are already rich and with their coin POS, every week is like winning a lottery for those guys. Those from institutions are going to stake of course, these are the guys who want to make money using the money. Anyone would want to be part of the network to make money, it's the price that is preventing poor people from investing.
The recent news you can find today is that Vilatik is not staking his ETH. He sure is not like those guys.
Define huge holdings. Price is always relative, and number of "full coins" doesn''t matter. Just % of the tokens you own of the supply and value of them.
The fact that Vitalik isn't taking part to consensus is a very good thing, because his share of it (and the power coming with that) would be too big imho.