My question is : is it possible to keep 1 mb block (with technical solutions) while the transaction numbers per day increases to 1 million, 10 millions, 100 millions...?
I think that LIGHTNING NETWORK can make this possible because for every transaction channel where can happen unlimited transaction there is only one transaction happening on the BLOCKCHAIN. why some are skeptical about Lightning network?
I think that for the foreseeable future, the Lightning Network will be enough with Segwit's 4MB block weight limit. That assumes that routing is sufficient (not totally clear yet from testing).
But if we're talking about a 300-fold increase, I don't think anyone can give you a clear answer. It largely depends on what the topography and usage of the Lightning Network looks like, and if the vast majority of transactions can be taken off-chain in an efficient, trustless way. We need to wait and see.