what will be the effect on network and different technical metrics, if anyone sent 1 millions bitcoins in 1 transaction (hypothetically for now because no one have even 2% in one wallet)
If a situation like that were ever going to be possible, I said
ever going to be possible because there's no single wallet that hodls 1million BTC, it will only cause FUD in the market whose end product is dump. The good thing from such a situation will be that wealth will be recreated or redistributed. Every serious dump affords those who couldn't buy in at high to get in at low. That's how so many wallets get Bitcoin as against the few that hedl those quantities in the past.
No effect on the network at all, only I think if the sender is kind enough to set a very high fee for the miner's reward (as a billionaire) say 1000BTC for a single transaction, then it will probably be a record in bitcoin mining history using current price conversion.
I like records getting broken and history made. It will help widen our scope of discussion in this industry if that were ever going to be possible. Sadly, this won't happen.