What do you reckon the chances are that the Major altcoins set new ATHs against Bitcoin - sometime in the future?
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Major altcoins can but they need a support from Bitcoin.

Bitcoin need to give investors confirmation that it won't crash more and won't have a bear market that last for few years. After that confirmation, if Bitcoin moves side way, top altcoins can rise again.

If you see how YFI have a few fold higher than BTC , you will see top altcoins can reclaim their Satoshi all time highs. It is not easy.