The biggest crypto fund Grayscale Bitcoin Trust bought another 15 114 BTC last week and fund's crypto AUM is almost $10B with 506 000 BTC. In my opinion such BTC stockpiling can be dangerous like a 51% attack but I didn't find any information is Satoshi Nakomoto ever mentioned that.
506k is not a too big amount percent-wise. However as they accumulate more, the price of Bitcoin also raises so some of the assets will probably get liquidated at some point in time.
I'm glad to see that they continue aggressive buying of Bitcoin. This shows the confidence they have in the cryptocurrency. Regarding the 51% attack, I don't think we should worry. They would have to own 51% of the mining power, not of the Bitcoin in circulation AFAIK to perform. Even in an abstract case, it would be counterproductive to invest all this money into the cryptocurrency in order to perform an attack on it
