The hash of a block can not be fake it, the only way to produce an exact hash of a block (hash+tx) is that all data of the block (tx) is exactly the same, if you change 1 tx, that will generate a new hash for the block, so, in terms of faking a block hash is nearly impossible.
I do not understand what
thqt means, but in term of time consuming when the blockchain got like 5 millions of blocks (actual blockchain is around 650000 of blocks), I think this is not going to be an issue at all, looking back into the blockchain, first of all, the actual blockchain is around 300gb, thats not too much for more than 10 years of data. Secondly, technology always improve faster in terms of hardware, meaning that next PCs will have more RAM, CPU (cores + instructions), Storage (SSD is faster than HDD for example)…My point is, looking into the blockchain some data really old, will never be time consuming enough for a high-end PC.
So I think bitcoin blockchain will never be an issue in terms of how much could the blockchain be limited in size, or what if it’s so long that is hard/slow to read…
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