....(before transparent forging was partly implemented at block height 30000, in the current version the account that will forge the next block is already known, you don't have enough time to produce a valid block and influence the desired next forging account, you would need huuuge amounts of computing power to do so).

You need to provide mathematical proof of how much cumputing power is needed to build a long enough chain and trick the network to accept your fake chain. I say (sorry only speaking about Nxt again) you'd need too much. Prove me wrong.

And Nxt does not use coin age, which released minting power to the account that signed the block, if the block was orphaned. So that attack vector is also gone.